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we derive an analytic approximation for the emissivity of neutrino-pair bremsstrahlung (npb) due to scattering of electrons by atomic nuclei in a neutron star (ns) crust of any realistic composition. the emissivity is expressed through generalized coulomb logarithm by introducing an effective potential of electron-nucleus scattering. in addition, we study the conditions at which npb in the crust is affected by strong magnetic fields and outline the main effects of the fields on neutrino emission in nss. the results can be used for modelling of many phenomena in nss, such as cooling of young isolated nss, thermal relaxation of accreting nss with overheated crust in soft x-ray transients and evolution of magnetars. | an effective potential for electron-nucleus scattering in neutrino-pair bremsstrahlung in neutron star crust |
thorne-żytkow objects (tżos) are a theoretical class of star in which a compact neutron star is surrounded by a large, diffuse envelope. supergiant tżos are predicted to be almost identical in appearance to red supergiants (rsgs), with their very red colors and cool temperatures placing them at the hayashi limit on the h-r diagram. the only features that can be used at present to distinguish tżos from the general rsg population are the unusually strong heavy-element and lithium lines present in their spectra. these elements are the unique products of the stars fully convective envelope linking the photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. we have recently discovered a tżo candidate in the small magellanic cloud. it is the first star to display the distinctive chemical profile of anomalous element enhancements thought to be characteristic of tżos however, up-to-date models and additional observable predictions (including potential asteroseismological signatures) are required to solidify this discovery. the definitive detection of a tżo would provide the first direct evidence for a completely new model of stellar interiors, a theoretically predicted fate for massive binary systems, and never-before-seen nucleosynthesis processes that would offer a new channel for heavy-element and lithium production in our universe. | discovery of a thorne-żytkow object candidate in the small magellanic cloud |
we propose to continue our very successful program to use the observed cooling of the crusts in transiently accreting neutron star x-ray binaries to probe the behavior of ultra-dense matter. those crusts are heated due to the accretion of matter during the outbursts of those transients. after the outbursts are over the crusts cool until they are in equilibrium with the cores again. following this cooling process for several systems has given us important insights in the structure of neutron stars, but many uncertainties remain. therefore it is needed to enlarge our sample to obtain better insights in the behavior of how neutron stars react to the accretion of matter. our program combines the strengths of chandra and xmm-newton and has proven to be excellently suited to obtain those goals. | crust cooling of accretion-heated neutron stars |
black hole-accretion disk systems from compact binary mergers are possible engines for short duration gamma-ray bursts (grbs). in this scenario the evolution of the post-merger remnant torus is determined by a combination of neutrino cooling and magnetically-driven heating processes. we study the post-merger evolution of a magnetized black hole-neutron star binary system using results from a previous numerical relativity simulation and einstein's spectral code's mhd module. we use finite-temperature tabulated equation of state, and leakage scheme to study the neutrino effects. in order to check the reliability of our results, we evolve the system with two different numerical methods: 1) using the cubed-sphere multipatch grids with an improved method for thermal evolution, dealing with supersonic accretion flows more accurately, and 2) using the cartesian grid with spec's conservative mhd formalism. we find that a seed magnetic field triggers a sustained source of heating, but its thermal effects are largely cancelled by the advection cooling and expansion of the torus from the mhd-related effects. | evolution of the magnetized, neutrino-cooled accretion disk in the aftermath of a black hole neutron star binary merger |
we propose a 45-ks chandra observation to continue our monitoring of the quiescent neutron star x-ray binary exo 0748-676. a 25-year long accretion outburst severely heated the neutron star crust, which has been gradually cooling since the source returned to quiescence in 2008. monitoring this thermal evolution provides the unique opportunity to study the heating processes and thermal transport properties of the neutron star crust. in addition we propose for 9 orbits of hst time to investigate the uv spectrum of exo 0748-676 to disentangle its quiescent accretion stream. this is of vital importance for a correct interpretation of the quiescent thermal x-ray emission and hence of the observed crust cooling. | the x-ray and uv spectra of the quiescent neutron star x-ray binary exo 0748-676 |
we study the v\bar v-pair emission from electrons and protons in a relativistic quantum approach. in this work we calculate the luminosity of the v\bar v-pairs emitted from neutron-star-matter with a strong magnetic field, and find that this luminosity is much larger than that in the modified urca process. the v\bar v-pair emission processes in strong magnetic fields significantly contribute to the cooling of the magnetars. | neutrino and antineutrino pair-emission in strong magnetic field in relativistic quantum approach |
near infrared (nir) flare/rebrightening in the afterglow of the short hard gamma ray burst (shb) 130603b measured with the hubble space telescope (hst) and an alleged late-time x-ray excess were interpreted as possible evidence of a neutron-star merger origin of this shb. however, the x-ray afterglow that was measured with the swift-xrt and newton xmm have the canonical behaviour of a synchrotron afterglow produced by a highly relativistic jet. the h-band flux observed with hst 9.41 days after burst is that expected from the measured late-time x-ray afterglow. a late-time flare/re-brightening of a nir-optical afterglow of shb can be produced by jet collision with an interstellar density bump, or by a kilonova, but jet plus kilonova can be produced also by the collapse of compact stars (neutron star, strange star, or quark star) to a more compact object due to cooling, loss of angular momentum, or mass accretion. | grb 130603b: no compelling evidence for neutron star merger |
based on the special relativistic hydrodynamic equations and updated cooling function, we investigate the long-term evolution of neutron stars merger (nsm) remnants by a one-dimensional hydrodynamic code. three nsm models from one soft equation of state, sfho, and two stiff equations of state, dd2 and tm1, are used to compare their influences on the hydrodynamic evolution of remnants. we present the luminosity, mass and radius of remnants, as well as the velocity, temperature and density of shocks. for a typical interstellar medium (ism) density with solar metallicity, we find that the nsm remnant from the sfho model makes much more changes to ism in terms of velocity, density and temperature distributions, compared with the case of dd2 and tm1 models. the maximal luminosity of the nsm remnant from the sfho model is 3.4 × 1038 erg s-1, which is several times larger than that from dd2 and tm1 models. the nsm remnant from the sfho model can maintain high luminosity (>1038 erg s-1) for 2.29 × 104 yr. furthermore, the density and temperature of remnants at the maximal luminosity are not sensitive to the power of the original remnant. for the ism with the solar metallicity and nh = 1 cm- 3, the density of the first shock ∼10-23 g cm-3 and the temperature ∼3 × 105 k in the maximal luminosity phase; the temperature of the first shock decreases and there is a thin 'dense' shell with density ∼10-21 g cm-3 after the maximal luminosity. these characteristics may be helpful for future observations of nsm remnants. | hydrodynamic evolution of neutron star merger remnants |
superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. present theoretical calculations employ the quasi-particle mean-field hartree-fock-bogoliubov theory with temperature dependent occupation numbers for the quasi-particle states. finite temperature stellar matter is characterized by a whole distribution of different nuclear species. we want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. following a recent work, the wigner-seitz cell is mapped into a model with cluster degrees of freedom. the finite temperature distribution is then given by a statistical collection of wigner-seitz cells. we additionally introduce pairing correlations in the local density bcs approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. the heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 kev to 2 mev. we show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. we additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity. | the heat capacity of the neutron star inner crust within an extended nse model |
the observation of thermal emission from isolated neutron stars and the modeling of the corresponding cooling curves has been very useful to get information on the properties of matter at very high densities. more recently, the detection of quiescent thermal emission from neutron stars in low mass x-ray binary systems after active periods opened a new window to the physics of matter at lower densities. here we analyze a few sources that have been recently monitored and we show how the models can be used to establish constraints on the crust composition and their transport properties, depending on the astrophysical scenarios assumed. | inferring neutron stars crust properties from quiescent thermal emission |
both the symmetry energy part and excluded volume corrections to the equation of state play an important role for the neutron star interior structure and composition, namely for the profile of the baryon density and the proton fraction. while the symmetry energy uniquely determines the proton fraction, excluded volume effects control the maximum density values inside neutron stars. observations of cooling neutron stars indicate that the fast direct urca cooling is not operative for the typical, low mass stars, pointing at proton fractions that lie below the threshold for the onset of direct urca cooling process. this in turn, restricts the density range admissible in neutron star interiors and may require an excluded volume correction. in this contribution we discuss the interplay between fast cooling, symmetry energy and excluded volume corrections to the equation of state that would be required to fulfil the direct urca cooling constraint. | interplay between symmetry energy and excluded volume corrections under the direct urca cooling constraint in neutron stars |
neutron star mergers provide us with a remarkable laboratory to test the laws of physics in dense environments, to constrain the production sites of heavy elements, and to understand high-energy transients like gamma-ray bursts. neutrinos play an important role in these mergers: they are the main source of cooling in post-merger remnants, and the main drivers of changes to the composition of the matter that they eject. as a result, neutrino-matter interactions significantly impact the outcome of nucleosynthesis in mergers, and the properties of the optical/infrared transients that they power. most merger simulations to-date have however treated neutrinos using approximate transport methods - either ''leakage'' of ''moment'' schemes. here, i will discuss the implementation in the spec code of a monte-carlo transport scheme, the challenges associated with the use of such an algorithm in merger simulations, and its application so far to simulations of nsns and nsbh mergers. these simulations allow us to provide improved estimates for the properties of the baryonic matter ejected by mergers and of the neutrinos escaping merger remnants. comparisons with simulations using approximate transport algorithms also allow us to estimate uncertainties in these approximate transport schemes. the author gratefully acknowledges support from the doe through grant de-sc0020435, from nasa through grant 80nssc18k0565, and from the nsf through grant phy-1806278. | monte-carlo radiation transport in neutron star merger simulations |
the 1 km thick crust of neutron stars is strongly heated by nuclear reactions during accretion outbursts, but cools in quiescence. hete j1900.1-2455 continously accreted since 2005, but in 2015 late oct its intensity dropped below the detection limit of maxi. swift observations (mar 7) fail to detect the source, implying lx<e32 erg/s (0.5-10 kev) and a very cold neutron star crust of kt<65 ev. this is highly unexpected, as the crust should have been significantly heated during the 9 yr outburst: our studies of 5 other sources after >1 yr outbursts revealed hot neutron star crusts of >100 ev. this remarkable result suggests that nuclear heating may not always be efficient, a scenario that has never been considered to explain exceptionally cold neutron stars such as sax j1808.4-3658 and 1h1905+000. with a 30 ks ddt, we can put firm constraints on the crust temperature in hete j1900 (kt 33 ev; lx 2e30 erg/s), with important implications for neutron star heating/cooling models. | an exceptionally cold neutron star in hete j1900.1-2455 |
strongly interacting fermions define the properties of complex matter throughout nature, from atomic nuclei and modern solid state materials to neutron stars. ultracold atomic fermi gases have emerged as a pristine platform for the study of many-fermion systems. in this poster we demonstrate the realization of a quantum gas microscope for fermionic 40 k atoms trapped in an optical lattice and the recent experiments which allows one to probe strongly correlated fermions at the single atom level. we combine 3d raman sideband cooling with high- resolution optics to simultaneously cool and image individual atoms with single lattice site resolution at a detection fidelity above 95%. the imaging process leaves the atoms predominantly in the 3d motional ground state of their respective lattice sites, inviting the implementation of a maxwell's demon to assemble low-entropy many-body states. single-site resolved imaging of fermions enables the direct observation of magnetic order, time resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. nsf, afosr-pecase, afosr-muri on exotic phases of matter, aro-muri on atomtronics, onr, a grant from the army research office with funding from the darpa ole program, and the david and lucile packard foundation. | quantum gas microscope for fermionic atoms |
we used high-resolution spectra of all bright (v<8mag) f5 and cooler stars (teff<6500k) in several selected sky fields near the north ecliptic pole including tess northern continuous viewing zone (cvz). we used the 1.65m telescope at the moletai astronomical observatory of vilnius university in lithuania that is equipped with the high-resolution vilnius university echelle spectrograph (vues). this spectrograph has a wavelength coverage from 400 to 900nm. for our work, we used the r~68000 mode for the m spectral type stars and the r~36000 mode for other objects. (1 data file). | vizier online data catalog: abundances of neutron-capture elements (tautvaisiene+, 2021) |
we are developing a concept for a new canadian-led x-ray observatory — colibrì. the main objectives of the colibrì mission are to study the structure of accretion flows in the near vicinity of black holes and neutron stars, the emission from the surfaces of neutron stars, and the intergalactic medium. the colibrì concept concept is based on multiple aperture x-ray optics with cryogenically cooled transition-edge detectors for high energy resolution, time resolution, throughput and sensitivity from 100 ev to 15 kev. funded by the canadian space agency. | the colibri x-ray telescope |
the cooling behavior of neutron stars (nss) is a key observational test of the physics of their interiors, which can be probed through x-ray observations. while nss are hot enough to be studied in the x-ray, their long-term cooling is dominated by neutrino emission from the core. this enables us to constrain the neutrino emission processes in ns cores by studying their thermal x-rays. young nss, cooling after their birth in supernovae, provide the most straightforward tests of cooling theories. the diversity in their cooling tracks requires some variation in e.g. envelope composition. the youngest galactic ns, in cassiopeia a, may show evidence for rapid cooling, which if correct may indicate that neutrons in its core are transitioning to a superfluid state. however, monitoring its cooling taxes the limits of our observational capabilities, and it is not certain that the apparent flux decline actually indicates cooling.old nss in x-ray binaries can also be used to probe cooling, by comparing their thermal surface emission (heat going out from the surface) with their long-term time-averaged accretion history (heat deposited inside), to determine the rate at which neutrinos must be removing heat from the core. note that nss also experience short-term cooling after episodes of intense accretion, which reveals information on the properties of the crust (see cumming's talk). intriguingly, a wide range of neutrino emission rates appear to be present within nss in x-ray binaries. this wide range can be most easily explained if nss have a wide range of masses, and if the most massive, and thus densest, nss can access faster neutrino cooling mechanisms (such as the direct urca process) in their cores. | neutron star cooling |
previous studies of the young (340 yr) central compact object (cco) in the cas a supernova remnant resulted in a reported decrease of the cco's surface temperature by about 2% in 10 years. however, the actual rate of this exceptional cooling is still uncertain as the most recent data hint at a puzzling difference between cooling trends in early and later years. in order to constrain the cooling rate more accurately, we propose to continue the monitoring of the thermal evolution of this neutron star. the legacy time series of the cas a cco provides a crucial checkpoint for theoretical models concerning the properties of the neutron star interior. | monitoring the thermal evolution of the cas a cco |
we propose to continue our very successful program to use the observed cooling of the crusts in transiently accreting neutron star x-ray binaries to probe the behavior of ultra-dense matter. those crusts are heated due to the accretion of matter during the outbursts of those transients. after the outbursts are over the crusts cool until they are in equilibrium with the cores again. following this cooling process for several systems has given us important insights in the structure of neutron stars, but many uncertainties remain. therefore it is needed to enlarge our sample to obtain better insights in the behavior of how neutron stars react to the accretion of matter. our program combines the strengths of chandra and xmm-newton and has proven to be excellently suited to obtain those goals. | crust cooling of accretion-heated neutron stars |
a neutron star is a highly dense object which lasts after a supernova explosion. the density of a neutron star overcomes the nuclear density, and the temperature is high at the beginning of its history. an isolated neutron star does not have any heat sources, and it cools down emitting thermal energy by neutrinos. the neutrino emission process depends on the state of interior matter of the neutron star. to compare theoretical simulations and observations of neutron stars, it can constrain the nuclear theory of high density region. we create a model of neutron stars with colour superconducting quark matter and nucleon superfluidity/superconductivity, to satisfy recent observations, including two 2m ⊙neutron stars. we parameterize these super-states and demonstrate the cooling curves, which show heavy stars do not always cool faster than lighter stars. | neutron star cooling with various superfluid and superconducting states |
we propose a 135 ks chandra observation of the globular cluster terzan 5, to continue our study of the thermal evolution of the transiently accreting neutron star igr j17480-2446. our previous chandra observations revealed that the crust of this neutron star was strongly heated during a 10-week long accretion outburst in 2010, and is currently cooling in quiescence. monitoring this cooling yields valuable information about the heat generation and thermal transport properties of the neutron star crust. following the first instance where crust cooling has been observed after a short accretion outburst poses a breakthrough opportunity in neutron star research: it opens up a new class of sources to study and to probe heat release at shallower depth than previously possible. | probing the physics of neutron stars using terzan 5 |
we analyze the effects of pairing correlations on the behavior of stellar matter, focusing on thermodynamical conditions close to the onset of the liquid-gas phase transition, which are characterized by quite large density fluctuations and where clustering phenomena occur. we concentrate on the neutrino transport properties and we show, within a thermodynamical treatment, that at moderate temperatures, where pairing effects are still active, the scattering of neutrinos in the nuclear medium is significantly affected by the matter superfluidity. the pairing correlations can indeed enhance neutrino trapping and reduce the energy flux carried out by neutrino emission. new hints about an important impact of pairing on the cooling mechanism, by neutrino emission, are so envisaged and therefore this study could be of relevant interest for the evolution of proto-neutron stars and in modelization of supernova explosions. | impact of pairing on clustering and neutrino transport properties in low-density stellar matter |
we propose to study the cooling of the neutron star crust in maxi j0556-332 after its most recent (fourth) outburst. of all cooling neutron stars in lmxbs, maxi j0556-332 has shown by far the strongest shallow heating. this is a process of unknown origin in the upper layers of the neutron star crust that dominates the energy release during the first years in quiescence. clues towards its origin come from three previous outbursts of maxi j0556-332, which hint at a surprising relation between outburst fluence and the heat release per accreted nucleon in the shallow heating process. this can be investigated further by obtaining good constraints on the shallow heating strength during its fourth outburst. to this end we request a 45 ks chandra observations of the source early in cycle 23. | shallow heating in the neutron star crust of maxi j0556?-332 |
the central compact object (cco) in the cas a snr is a 340 yrs old neutron star. a decrease of its surface temperature by at least 2% in 10 years has been reported, on an 18 years baseline. the used acis data were affected by time-dependent instrumental effects (particularly pileup). the unknown time-dependent systematic errors make it difficult to assess the significance level of the decrease. the results from acis observations in a more suitable mode were consistent with a constant temperature. in order to increase the time coverage of such data with minimized systematic effects from 8.5 to 14.5 years, we propose a new monitoring observation. tightly constraining the cooling of the cco will have profound consequences for our understanding of fundamental properties of matter. | monitoring the thermal evolution of the cas a cco |
weak decay processes (like direct and modified urca) play an important role in transport phenomena in neutron stars and neutron star mergers. the traditional treatment for the in-medium nucleon propagator in the modified urca process uses crude approximations. we are developing an approach to unify direct and modified urca processes by including the nucleon widths. this potentially allows us to improve several aspects of the urca rates, which can influence cooling, bulk viscosity and other dissipative processes. this research was partly supported by the u.s. department of energy, office of science, office of nuclear physics, under award no. #de-fg02-05er41375. | a unified approach to urca processes |
what is the heaviest element that can, if it is very short lived, exist in nature? this simple, yet profound question has urged us to synthesize unknown superheavy nuclei (shn) at terrestrial accelerator facilities all over the world. the synthesis of shn is notoriously difficult due to its really tiny cross sections on the order of picobarn to femtobarn. while the cold fusion reactions, which take advantage of the stabilization effect of doubly-magic 208pb or its neighbor 209bi, reducing excitation energy of a compound system, have been successful to synthesize shn up to the element 113, nihonium, it suffers from an exponential decrease of the cross section with increasing the proton number z. on the other hand, the hot fusion reactions employ a neutron-rich calcium isotope, 48ca, as a projectile with an actinide target, leading to higher excitation energy as compared to the cold one, while subsequent neutron evaporation successfully cools it down. the latter sustain picobarn-level cross sections even for z >113 and up to the element 118, oganneson, have been synthesized so far. although those artificially synthesized shn are short-lived, their chemical as well as nuclear properties are of great interests, offering a unique opportunity to challenge our theoretical understanding. if it is really difficult to synthesize shn experimentally, why don't we look for other possibilities, e.g., naturally existing shn somewhere in the universe? that is the topic i would like to discuss in this talk. recently, we have investigated effects of a superstrong magnetic field (as large as 1018 g) on compositions of the outer crust of neutron stars and found that extremely neutron-rich shn, including yet unknown elements, emerge as an equilibrium composition of the outer crust of a strongly-magnetized neutron star [1]. the main cause of the emergence of shn is the landau-rabi quantization of electron motion perpendicular to the magnetic field, which enhances the electron (and, thus, proton) fraction, allowing for the outer crust to extend at a higher pressure (density) region. in this talk, i will discuss implications of the finding, building a new bridge between the studies of shn and neutron stars. this work is supported by jsps grant-in-aid for scientific research, grant nos. 23k03410 and 23h01167. | a new perspective of the study of superheavy nuclei |
this study presents multiphysics analyses of the electron target cooling system of the accelerator-driven system (ads) of the kharkiv institute of physics and technology (kipt) using mcnp and fluent computer programs. mcnp has been used to transport electrons, gammas, and neutrons, and to calculate the energy deposition in the target materials. the mcnp mesh-tally data have been imported into fluent by a c subroutine that has been compiled and linked to fluent as a user-defined function. the kipt ads is located in ukraine and was in operation until february 2022. the fluent model is based on the computer-aided design files from the manufacturing process of the target assembly. the fluent results for the reference case match very well the literature results obtained by star-ccm+ during the design phase. other cases that differ from the reference one have been analyzed; in these cases, it is assumed a malfunction of the electron accelerator or of the water cooling system. the target cooling system operates normally for all the analyzed cases except when the inlet water mass flow rate is decreased. the transient analysis showed that the target cooling system can operate for 180 s with full power when the inlet water mass flow rate is decreased down by 75%. | electron target cooling analyses of the kipt ads using mcnp and ansys fluent |
this paper presents the theory and application of a code called callisto which is used for performing npp start-up and power ascension calculations. the callisto code is designed to calculate various values relating to the neutron population of a nuclear system which contains a low number of neutrons. these variables include the moments of the pdf of the neutron population, the maturity time and the source multiplier. the code itself is based upon the mathematics presented in another paper and utilises representations of the neutron population which are independent of both space and angle but allows for the specification of an arbitrary number of energy groups. five examples of the use of the code are presented. comparison is performed against results found in the literature and the degree of agreement is discussed. in general the agreement is found to be good and, where it is not, plausible explanations for discrepancies are presented. the final two cases presented examine the effect of the number of neutron groups included and finds that, for the systems simulated, there is no significant difference in the key results of the code. | callisto-spk: a stochastic point kinetics code for performing low source nuclear power plant start-up and power ascension calculations |
unlike the commonly known rotation-powered pulsars, x-ray thermal isolated neutron stars (xtinss) do not show radio/gamma-ray emission or other signs of magnetospheric activity but emit purely thermal soft x-ray radiation. a few hst observations of these sources have shown very puzzling results, with possible contribution from neutron star magnetospheres or fallback disks, challenging the simplistic model of a purely thermal emitter. however, because most xtinss only have hst coverage in two spectral bands, the actual spectral shape and the origin of the xtins uv-optical-ir emission remain unknown. rx j1243.0+0654, the most intriguing xtins, provides the best opportunity to clarify the origin of the xtins emission. we propose photometric measurements with high s/n in five spectral bands in the wavelength range of 0.14-1.7 microns. fits of the five flux density points with different spectral models will help to understand the nature of this and other xtinss. using the same observations, we will also check for long-term variability of the target in two bands and measure its (currently unknown) proper motion with an uncertainty not exceeding 2 mas/yr, much lower than expected proper motion values. this will allow us to locate the birth place of this neutron star and estimate its kinematic age. these properties are required to constrain the neutron star cooling models and learn about evolutionary links between the diverse neutron star populations. | the most puzzling uv-optical-nir spectrum of an isolated neutron star: a disk or a magnetosphere? |
we discuss the effect of the chemical composition of heat blanketing envelopes of neutron stars (nss) on the interpretation of the observations of these stars. first we analyze the diffusive fluxes of ions in non-isothermal and non-ideal coulomb plasmas. then we outline models of diffusively-equilibrated heat blanketing envelopes composed of binary ionic mixtures and finally we study their effect on the cooling of isolated nss. | heat blanketing envelopes vs cooling of neutron stars |
neutron stars are high-density objects formed by the gravitational collapse of massive stars, and the whole star can be likened to a giant nucleus. the interior of a neutron star is considered to contain exotic particles and states which do not appear in a normal nucleus. the internal states are constrained by observations of masses and radii via the equation of state of highly dense nuclear matter. within these constraints, a variety of exotic states have been discussed. the internal state of neutron stars is closely related to its neutrino emission process, which cools the star from the inside. this effect can be compared with observations of the surface temperature of neutron stars. however, despite the wide range of observations of neutron stars, the nature of the neutron star matter remains uncertain. we consider quark matter as an exotic state and perform cooling calculations for neutron stars, incorporating the effects of nucleon superfluidity and quark colour superconductivity.we take into account the "quark-hadron continuity", in which the neutron superfluidity is succeeded by thedquark pairing. furthermore, we obtained the range of the neutron star cooling curve, taking into account the difference in surface temperature due to the composition of the surface layer. we found that the existence of quark matter causes strong neutrino emission from quarks, which is moderately suppressedbysuperfluidity and superconductivity, and canexplain the cold surface temperature of neutron stars. | cooling of neutron stars with quark-hadron continuity |
the direct urca process of rapid neutrino emission can occur in nonuniform nuclear pasta phases that are expected in the inner crust of neutron stars. here, the periodic potential for a nucleon in nuclear pasta allows momentum conservation to be satisfied for direct urca reactions. we improve on earlier work by modeling a rich variety of pasta phases (gnocchi, waffle, lasagna, and anti-spaghetti) with large-scale molecular dynamics simulations. we find that the neutrino luminosity due to direct urca reactions in nuclear pasta can be 3 to 4 orders of magnitude larger than that from the modified urca process in the neutron star core. thus neutrino radiation from pasta could dominate radiation from the core and this could significantly impact the cooling of neutron stars. | fast neutrino cooling of nuclear pasta in neutron stars: molecular dynamics simulations |
as an advanced research tool, neutronics and thermal-hydraulics coupling have a wide range of promising applications in the field of nuclear energy. this paper develops a burnup-control drum coupling code based on the monte carlo code rmc and the computational fluid dynamics (cfd) program star-ccm +. the dynamic adjustment of the control drums' position and more realistic prediction of reactor neutronics and thermal-hydraulics is achieved by updating the nuclide density, solving the control drum value function and updating the neutronics model in the process of burnup calculation. the core of a lead-bismuth-cooled solid reactor was also studied to investigate the neutronics and thermal-hydraulics properties of the solid core when the effective multiplication factor was kept at about 1.0, and the core's power and temperature variation patterns during the lifetime were obtained. the results of the study show that the simulation of the coupling code achieves the design purpose. in addition, the solid core's maximum fuel and cladding temperatures decrease with the deepening of the burnup. | burnup-control drum coupling characteristics investigation of lead-bismuth eutectic-cooled solid reactor |
neutron-rich matter exists naturally in neutron stars and some nuclei. it can also be created during mergers of neutron stars in space and collisions between two heavy nuclei in terrestrial nuclear laboratories. the nature and equation of state (eos) of such matter are still very poorly known while they have broad impacts on many interesting issues in both astrophysics and nuclear physics. in particular, nuclear symmetry energy encoding the energy cost to make nuclear matter more neutron rich has been the most uncertain part of the eos of dense neutron-rich nucleonic matter. it affects the masses, radii, tidal deformations, cooling rates and frequencies of various oscillation modes of isolated neutron stars as well as the strain amplitude and frequencies of gravitational waves from neutron star mergers. in this talk, we will first review some recent progresses in constraining nuclear symmetry energy up to about twice the saturation density of nuclear matter especially since gw170817 and then discuss possible causes for the still very uncertain high-density symmetry energy. as an example, we examine the role of tensor force induced nucleon- nucleon short-range-correlations (src) on the high-density behavior of nuclear symmetry energy. this work is supported in part by the u.s. department of energy, office of science, under award no. de-sc0013702. | probing symmetry energy of dense neutron-rich matter |
neutron stars are heated during accretion episodes due to nuclear reactions that occur in their crust, while they cool primarily through neutrino emissions from their core. during quiescence, the thermal glow of a neutron star can be detected with sensitive x-ray satellites. comparing the observed thermal quiescent x-ray emission with heating and cooling models provides valuable insight into the interior properties of neutron stars, such as the composition and superfluid properties of their dense cores. here we propose 30-ks chandra observations of three neutron stars that have very low time-averaged accretion rates. by investigating their quiescent thermal luminosity, we aim to probe a completely unexplored regime for neutron star heating and cooling models. | an unexplored regime of neutron star heating and cooling |
compact binary mergers involving at least one neutron star are promising sites for the synthesis of r-process elements found in stars and planets. however, mergers can take place at significant offsets from their host galaxies, with many occurring several kpc from star-forming regions. it is thus important to understand the physical mechanisms involved in transporting enriched material from merger sites in the galactic halo to the star-forming disk. we investigate these processes, starting from an explosive injection event and its interaction with the halo medium. we show that the total outflow mass in compact binary mergers is too low for the material to travel to the disk in a ballistic fashion. instead, the enriched ejecta is swept into a shell, which decelerates over ≈10 pc scales and becomes corrugated by the rayleigh-taylor instability. the corrugated shell is denser than the ambient medium, and breaks into clouds which sink toward the disk. these sinking clouds lose thermal energy through radiative cooling, and are also ablated by shearing instabilities. we present a dynamical heuristic that models these effects to predict the delay times for delivery to the disk. however, we find that turbulent mass ablation is extremely efficient, and leads to the total fragmentation of sinking r-process clouds over 10−100 pc scales. we thus predict that enriched material from halo injection events quickly assimilates into the gas medium of the halo, and that enriched mass flow to the disk could only be accomplished through turbulent diffusion or large-scale inflowing mass currents. | r-process rain from binary neutron star mergers in the galactic halo |
a method of uncertainty quantification in the calculation of wait-time probability distributions in delayed supercritical systems is presented. the method is based on monte carlo uncertainty quantification and makes use of the computationally efficient gamma distribution method for prediction of the wait-time probability distribution. the range of accuracy of the gamma distribution method is examined and parameterised based on the rate and magnitude of the reactivity insertion, the strength of the intrinsic neutron source and the prompt neutron lifetime. the saddlepoint method for inverting the generating function and a monte carlo simulation are used as benchmarks against which the accuracy of the gamma distribution method is determined. finally, uncertainty quantification is applied to models of the y-12 accident and experiments of authier et al. (2014) on the caliban reactor. | importance of parametric uncertainty in predicting probability distributions for burst wait-times in fissile systems |
we present results from fully relativistic simulations of binary neutron star mergers varying the tabular equation of state used to approximate the degenerate material and the mass ratio. the simulations incorporate both magnetic fields and the effects of neutrino cooling. in particular, we examine the amount and properties of material ejected from the merger. we gratefully acknowledge the support of nasa through the astrophysics theory program grant nnx13ah01g. | mergers of binary neutron star systems |
recently, it has been discovered that the beta+decay rates and neutrino loss rates of 64ga and 68se greatly affect the light curves and final abundances of x-ray bursts in a one-zone model in all circumstances. here we further expand the study to the multizone model mesa and compare the results with observations of the bursting source gs 1826-24. it was found that the light curve of the modified beta decay rates of 64ga is more comparable to observations than the standard beta decays. the final mass fractions of the ashes of the x-ray bursts for elements with a mass number of 38 (38ar, 38ca) are greatly modified because of the beta+decay rate and neutrino loss rate of 68se. they also produce more urca nuclei, which may lead to stronger cooling in the neutron star crusts. both the modified rates of 68se and 64ga make the recurrence times of the simulated x-ray bursts longer because they cause more energy loss than the standard rates and more time is needed to accumulate energy to trigger the bursts. | sensitivity studies on the thermal beta+decay and thermal neutrino loss rates in the multizone x-ray burst model mesa |
the equation of state (eos) for nuclear matter at finite temperature and out of equilibrium is a fundamental ingredient for simulations of binary neutron star mergers, calculation of cooling curves, and other transport properties. we construct four new eoss using a relativistic mean-field theory (rmf). typically, the couplings in an rmf are fit to isospin-symmetric nuclear matter data, but the matter in isolated neutron stars is much closer in composition to pure neutron matter. in this work, along with reproducing isospin-symmetric nuclear matter data, we also fit our rmf to pure neutron matter calculations from chiral effective field theory. these calculations are needed because it is not possible to perform experiments on pure neutron matter on earth. our eoss agree with current mass and radius measurements from nicer and ligo. | equations of state at finite temperature and out of equilibrium calibrated using chiral effective field theory |
this paper describes a novel methodology for the analysis of nuclear criticality excursions in fissile powder beds under wetting conditions. these potentially hazardous powder, slurry and sludge systems may be found in nuclear fuel manufacturing and fabrication facilities. a point neutron kinetics model was coupled with water infiltration, thermal-hydraulics and radiolysis models through the use of reactivity feedbacks. good agreement in the water infiltration rate was found when comparing the water infiltration model used in this paper to experiments conducted by the french commissariat à l'énergie atomique et aux énergies alternatives (cea). a case study was proposed whereby a sheet of fine water droplets from a sprinkler system came into contact with an open-topped bed of low enriched uo2 powder. simulations indicate that the mean powder particle size had a strong effect on the time required for the water to percolate through the powder bed. powder particle size was also predicted to have a moderate effect on the initial fission power spike. the fission energy released over the first 300 s of the nuclear criticality transient ranged from 65.28 mj to 97.98 mj depending on mean powder particle size. this is similar in magnitude to other simulated nuclear criticality excursions in powder beds. the model predicts that the initial fission power spike would be limited by the production of radiolytic gas and to a lesser extent the effects of doppler broadening and thermal expansion. as expected, boiling and the associated steam production, was found to be an important phenomenon in the reduction of the fission rate through the negative void reactivity effect of the steam. | mathematical and computational models for simulating transient nuclear criticality excursions within wetted fissile powder systems |
this paper describes a probabilistic method of modelling point nuclear systems with low numbers of neutrons including the effects of delayed neutron precursors and its coupling with standard point kinetics equations. this coupling allows the simulation of the non-deterministic progression of a system transitioning from subcritical to supercritical and the resulting power peak. through analysis of large numbers of realisations various statistical parameters of such transients can be obtained. the method of simulation presented here successfully replicates the survival and extinction probabilities predicted by the backwards master equation and experimental and analytic results from the literature regarding the godiva reactor and extends the examination of that reactor. in particular the effect of delayed neutrons on the simulated response of godiva is highlighted. with its implementation in a parallel computer code, the model is able to simulate at a reasonable speed a range of systems where low neutron populations are important. | coupled probabilistic and point kinetics modelling of fast pulses in nuclear systems |
we propose to observe the tev-emitting supernova remnanthess j1731347for 36 ks to measureits expansion rate by comparing the new image of the x-ray filaments with that obtained in 2008. we willalso search for variability within filaments, and measure the displacement between the remnants centralneutron star and its former binary companion. the measurements will be used to constrain the forward shockspeed, the magnetic field strength at the x-ray emitting filaments, the density of the ambient medium, the ageof the remnant, and the cooling properties of the central neutron star. | constraining the expansion rate of the supernova remnant hess j1731-347 |
the doppler beaming effect for cool stars is amplified relative to a blackbody of the same temperature because of deep tio and vo absorption features. also, a strong na feature at 5890a coincides with the short wavelength cutoff of the tess response function. we simulated doppler beaming for bt-settl model spectra ranging from 2600k to 5200k and with radial velocities of ± 400 km/s. for a 3000 k object, the change in flux was up to two times greater than predicted for a blackbody in the tess filter. we repeated the same simulation for the kepler/k2 and gaia filters and obtained a similar result. when using the photometric beaming amplitude to determine stellar properties, an underestimated doppler beaming coefficient results in mass overestimates. this is especially important for m dwarfs in short period binary systems with massive white dwarf, neutron star or black hole companions. the effect could also impact the photometry of runaway/hypervelocity m dwarfs. we present tess photometry of the pre-cataclysmic variable triple system wolf 1130 and confirm that the measured beaming amplitude of wolf 1130ab is nearly triple the theoretical expectation. | a source of uncertainty in tess photometry of high-velocity m dwarfs |
recent detections of high mass gravitational wave events in the upper neutron star mass range have raised the question, if near equal mass black hole -neutron star (bhns) systems could form and merge, and how they would be distinct from a binary neutron star merger. in this talk, i will present general-relativistic magnetohydrodynamics (grmhd) simulations of the merger and post-merger evolution of several near equal mass bhns systems covering the first 100-200 ms after merger. these simulations are among the few to self-consistently include the magnetic field during the merger and use finite-temperature equations of state and neutrino cooling effects. based on these simulations, i will comment on the general properties of the mass ejection, the magnetic field topology and the evolution of the remnant accretion disk. | near equal mass black hole - neutron star mergers: general-relativistic magnetohydrodynamics simulations with realistic microphysics |
although accretion disc coronae appear to be common in many accreting systems, their fundamental properties remain insufficiently understood. recent work suggests that type i x-ray bursts from accreting neutron stars provide an opportunity to probe the characteristics of coronae. several studies have observed hard x-ray shortages from the accretion disk during an x-ray burst implying strong coronal cooling by burst photons. i will present simulation results done with the plasma emission code eqpair to study the impact of x-ray bursts on coronae, and how the coronal and burst properties affect the coronal electron temperatures and emitted spectra. | cooling of accretion disc coronae by type i x-ray bursts |
neutrinos act as an important cooling mechanism in an array of explosive astrophysical events. modeling of their fluxes and spectra is key for the interpretation of their detection and the understanding of the synthesis of heavy elements. the neutrino surface is key in the modeling of neutrino spectra. in previous work, the points of last neutrino scattering were found assuming no interaction between nucleons. in this work we incorporate this interaction using a few different models and observe differences in where the neutrinos decouple from the system. | nucleon-nucleon interaction and the neutrino surface of neutron star mergers |
type i x-ray bursts are unstable nuclear burning processes that occur on the surface of neutron star in low-mass x-ray binary. the radiation of type i x-ray bursts can have significant effects on matter around neutron stars. we review the observations and theoretical interpretations of the interaction between type i x-ray bursts and matter around neutron stars, including the increased accretion rate caused by the poynting-robertson effect, the absorption edge features in the burst spectra, the accretion disk reflection features, the disappearance and emergence of the khz qpo(quasi-periodic oscillation) signal during bursts, the hard x-ray flux deficit due to the coronal cooling. furthermore, we also present recent progress from nicer observations. | the research progress of the interaction between type i x-ray burst and matter around neutron stars |
the goal of this study is to improve a micro reactor core into uniform power distribution, a smaller and safer core. neutronic thermal-hydraulics coupling is an effective means to study the characteristics of microreactors. this paper performs an improvement work of lead-bismuth eutectic alloy (lbe) cooled solid core using the three-dimensional neutronics/thermal-hydraulics coupling method. based on the monte carlo code rmc and the three-dimensional thermal-hydraulics code star-ccm+, the coupling code processes the power distribution, fuel temperature, coolant temperature, and coolant density. the improvement of the solid core is carried out in these aspects: reflector material, reflector dimensions, fuel materials, coolant channel dimensions, the volume fraction of fuel phase in dispersion fuel, and critical enrichment. this paper studies the effect of reflector material and dimensions on the solid core and its mechanism. after improvement, the power peaking factor is effectively reduced, while the size and weight of the solid core are also reduced than before due to the excellent ability of beryllium oxide (beo), making it compact and lightweight. in addition, the core eigenvalues keff and thermal characteristics of different ceramic fuels, uranium dioxide (uo2), uranium nitride (un), and uranium carbide (uc), are compared. uo2 was replaced by un, which improves the thermal conductivity and reduces the maximum temperature of the solid core. at the same pressure difference, the mass flow rate of the coolant and temperature distribution of the fuel and the variation trend of neutron characteristics are studied when the coolant channel diameter changes. the results indicate that the coolant channel diameter of 1.775 cm has the best safety effect on the core. the variation of critical enrichment and thermal conductivity of the fuel at different volume fractions is compared, and 60 % is chosen as the volume fraction of the fuel phase. the final design of the shutdown rod and control drums is performed to ensure that the core is subcritical under all conditions. the improved core can operate at full power for five years and is characterized by miniaturization, high thermal conductivity, low volumetric swelling rate, flattened power distribution, and abundant reactivity control measures. | improved design of lbe cooled solid reactor using 3d neutronics thermal-hydraulics coupling method |
neutron stars and magnetars possess extremely strong magnetic fields. radiative cooling of plasma particles in their magnetospheres can be short compared to the plasma dynamical time. such magnetospheres are observed to produce strong flares, which indicates production of a relativistic pair plasma. how does the particle distribution change as these particles propagate in the magnetospheric `magnetic trap'? here we discuss the motion of a relativistic charge in a straight magnetic trap subject to radiative energy loss. supported by the grants: doe de-sc0019474, nsf phy-2010109. | on motion of an charge in a magnetar magnetosphere |
the charge radius of 54ni was determined for the first time using collinear laser spectroscopy at the beam cooling and laser spectroscopy (becola) facility. combined with the known charge radius of its mirror partner 54fe, the slope l of symmetry energy in the nuclear equation of state was determined. the details of the experiment and the mirror-radius analysis will be presented. also, the obtained l will be compared with that obtained from the neutron star merger gw170817 and prex-2. this work was supported in part by grants nsf no. phy-15-65546, doe de-fg02-92er40750 and dfg sfb1245. | charge radius of neutron deficient 54ni and symmetry energy constraints using the difference in mirror pair charge radii |
some astronomical mysteries are found deep in the interiors of stars. such is the case with the puzzle of q-branch white dwarfs, a population of these evolved, dense stars that seems to have an unexpected heat source, causing them to cool more slowly than a typical white dwarf. one hypothesis proposes that q-branch white dwarfs gain extra heat from the rapid sedimentation sinking to the center of the star of neutron rich neon, 22ne. but recent molecular dynamics simulations conducted by matt caplan (illinois state u.), charles horowitz (indiana u.), and andrew cumming (mcgill u., canada) show that the tiny crystals of neon needed to speed up this sedimentation cant exist in a stable state in the interior of a typical white dwarf which means there must be some other mechanism at work heating q-branch white dwarfs. the image above shows the initial state of the authors simulations, in which a 22ne microcrystal (red) lies within a soup of carbon and oxygen (white) under the dense, high-pressure conditions that exist inside a white dwarf. to read more about the authors work, check out the article below.citationneon cluster formation and phase separation during white dwarf cooling, m. e. caplan et al 2020 apjl 902 l44. doi:110.3847/2041-8213/abbda0 | featured image: to heat a white dwarf |
we examine the frequencies of the gravitational waves radiating from the protoneutron star produced via the core‑collapse supernova. in a way similar to the cold neutron star, we find that the frequencies of the w1 and f mode gravitational waves can be, respectively, expressed well as a function of the stellar compactness and the stellar average density at each time step after core bounce. thus, via the simultaneous detection of both the f and w1 mode gravitational waves, one can determine the protoneutron star mass and radius at each time step. unlike the cold neutron star, the protoneutron star mass and radius are changing with time because of the mass accretion and cooling, which enables us to identify the equation of state for the high‑density region in principle via only one event of supernova. | gravitational waves from protoneutron stars and nuclear equation of state |
dense matter in neutron star crusts can be studied in transient low-mass x-ray binaries. in these systems, the accretion during outbursts compresses the underlying layers, heating the crust out of equilibrium with core. once the system is in quiescence, monitoring the thermal evolution of the crust allows us to probe dense matter physics. our recent observation of one such crust cooling source - exo 0748-676, exhibited an unexpected rise in surface temperature instead a further decay ~a decade after the end of its outburst. we request a ~60 ks chandra observation of this source in cycle 22 to infer the deep crustal physics resulting in this unusual behaviour. | investigating late-time evolution of exo 0748-676 |
super asymptotic giant branch (super-agb) stars reside in the mass range ~ 6.5-10 m⊙ and bridge the divide between low/intermediate-mass and massive stars. they are characterised by off-centre carbon ignition prior to a thermally pulsing phase which can consist of many tens to even thousands of thermal pulses. with their high luminosities and very large, cool, red stellar envelopes, these stars appear seemingly identical to their slightly more massive red supergiant counterparts. due to their similarities, super-agb stars may therefore act as stellar imposters and contaminate red supergiant surveys. the final fate of super-agb stars is also quite uncertain and depends primarily on the competition between the core growth and mass-loss rates. if the stellar envelope is removed prior to the core reaching ~ 1.375 m⊙, an o-ne white dwarf will remain, otherwise the star will undergo an electron-capture supernova (ec-sn) leaving behind a neutron star. we determine the relative fraction of super-agb stars that end life as either an o-ne white dwarf or as a neutron star, and provide a mass limit for the lowest mass supernova over a broad range of metallicities from the z=0.02 to 0.0001. | hiding in plain sight - red supergiant imposters? super-agb stars |
we present the results of chandra observations of two non-accreting millisecond pulsars psrs j1640+2224 (j1640) and j1709+2313(j1709), with low inferred magnetic fields in order to constrain their surface temperatures, obtain limits on the amplitude of unstable r-modes in them and make comparisons with similar limits obtained for a sample of accreting lmxb neutron stars (nss). we detect both pulsars in the x-ray band for the first time. we found upper limits on the global surface temperature of these pulsars that are ∼ 3.3 × 10^5 - 4.7 × 10^5k. these sources are several gyr old. in all standard cooling models nss cool to surface temperatures less than 10^4k in less than 10^7 yr. while we derived upper limits on the surface temperatures of these sources, they appear to be consistent with the values measured for psr j0437-4715 and j2124-3358. taken together these results suggest that the surface temperatures of at least some msps are significantly higher, given their ages, than standard cooling models would suggest. for pulsars that are inside the r-mode instability window, r-mode dissipation can provide a potential source of reheating. | where are the r-modes? chandra observations of millisecond pulsars |
neutron stars and magnetars possess extremely strong magnetic fields, so that radiative cooling of particles in their magnetospheres can be short compared to a plasma dynamical time. the magnetospheres are observed to produce strong flares, possibly due to reconnection, which is a source of high-energy particles. how does the particle distribution change as these particles propagate in the magnetospheric `magnetic bottle'? here we derive the equations that describe the motion of a relativistic `larmor particle' in a straight magnetic bottle subject to synchrotron energy loss. this result can be important for studies of a plasma around neutron stars and magnetars. supported by the nsf grant phy-2010109 and the doe epscor grant de-sc0019474. | on trapped particle motion in a strong magnetic field |
binary neutron star mergers can drive dynamical outflows of neutron rich material. these ejecta might be the astrophysical site of production of the r-process elements. in this talk, i will present very recent full-gr, numerical relativity, simulations of binary neutron star mergers with microphysical equation of state and a simplified treatment of neutrino radiation done with the whiskythc code. i will discuss the mechanisms driving the mass ejection, the role played by neutrino cooling and heating in shaping composition and morphology of the ejecta, as well as the impact on the final yields of the r-process nucleosynthesis. | dynamical ejecta from binary neutron star mergers |
hyperaccreting disks around black holes are the engines that drive outflows and jets in gamma ray bursts (grbs). the torus formed after the core collapse or a compact binary merger is composed of free nucleons, helium, electron-positron pairs, and is cooled by neutrinos rather than photon emission. hyperaccretion powers the ultra-relativistic jets, where the grb prompt emission originates. the neutrons produced in the disk and also in the outflowing material are necessary for the production of heavier nuclei. we discuss here the observable consequences of nucleosynthesis and we also apply the scenario of hyperaccretion to the gravitational wave source, gw150914. temporal coincidence reported by the fermi satellite suggested that the black hole merger might be accompanied with a grb. we propose that a collapsing massive star and a black hole in a close binary could lead to such event. gravitational wave emission due to the merger of collapsed core and the companion black hole might then coincide with a weak grb. | on the gamma-ray burst - gravitational wave association in gw150914 |
in this work, we present a calculation of the non-fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. the role of non-fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. we extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple fermi liquid case. | role of magnetic interactions in neutron stars |
both hot and cool evolved stars, e.g., red (super)giants and wolf-rayet stars, lose copious amounts of mass, momentum and mechanical energy through powerful, dense stellar winds. the interaction of these outflows with their surroundings results in highly structured and complex circumstellar environments, often featuring knots, arcs, shells and spirals. recent improvements in computational power and techniques have led to the development of detailed, multi-dimensional simulations that have given new insight into the origin of these structures, and better understanding of the physical mechanisms driving their formation. in this talk, i will discuss three of the main mechanisms that shape the outflows of evolved stars:- interaction with the interstellar medium (ism), i.e., wind-ism interactions- interaction with a stellar wind, either from a previous phase of evolution or the wind from a companion star, i.e., wind-wind interactions- and interaction with a companion star that has a weak or insignicant outflow (e.g., a compact companion such as a neutron star or black hole), i.e., wind-companion interactions.i will also highlight the broader implications and impact of these stellar wind interactions for other phenomena, e.g, for symbiotic and x-ray binaries, supernovae and gamma-ray bursts. | shaping the outflows of evolved stars |
the thermal evolution of neutron stars is a subject of intense research, both theoretical and observational. the evolution depends very sensitively on the state of dense matter at supranuclear densities, which essentially controls the neutrino emission. the evolution depends, too, on the structure of the stellar outer layers which control the photon emission. various internal heating processes and the magnetic field strength and structure will influence the thermal evolution. of great importance for the cooling processes is also whether, when, and where superfluidity and superconductivity appear within the neutron star. this article describes and discusses these issues and presents neutron star cooling calculations based on a broad collection of equations of state for neutron star matter and internal magnetic field geometries. x-ray observations provide reliable data, which allow conclusions about the surface temperatures of neutron stars. to verify the thermal evolution models, the results of model calculations are compared with the body of observed surface temperatures and their distribution. through these comparisons, a better understanding can be obtained of the physical processes that take place under extreme conditions in the interior of neutron | thermal evolution of neutron stars |
we calculate the neutrino mean free path in cold neutron matter with some modern brussels-montreal functionals. the three typical functionals used in this article produce quite different results implying a possible impact on the cooling mechanism of neutron stars. | neutrino mean free path in neutron matter with brussels-montreal skyrme functionals |
we study the dynamical evolution of the gravitational-wave driven instability of the f-mode in rapidly rotating relativistic stars. with an approach based on linear perturbation theory we describe the evolution of the mode amplitude and follow the trajectory of a newborn neutron star through its instability window. we study several evolutions with different initial rotation rates and temperature and determine the gravitational waves radiated during the instability. from the thermal evolution we find that the heat generated by shear viscosity during the saturation phase completely balances the neutrinos cooling and prevents the star from entering the regime of mutual friction. the evolution time of the instability is therefore longer and the star loses significantly larger amounts of angular momentum via gravitational waves. | the f-mode instability in relativistic neutron stars |
accretion flow around a black hole or a neutron star emits high energy radiations with varying spectral and temporal properties. observed temporal variations point to the existence of a mechanism, dictated by the flow dynamics and not by the stellar surface or magnetic fields, that is common in both types of compact objects. to investigate what can be the origin of such qpos in accreting neutron stars (ns), we use sph simulations to study inviscid and viscous flows, with cooling. the difference between accretion onto black holes (bhs) and nss is the presence of a hard surface for nss. we show that for an advective flow with nominal viscosity and angular momentum, the solution allows two shocks in the flow. the outer one forms due to a strong centrifugal barrier and is called centrifugal pressure dominated boundary layer (cenbol), which is a common feature for both nss and bhs. the inner shock or normal boundary layer (nbol) forms very close to the surface of an ns, due to the physical boundary. in presence of strong cooling, a disk is formed along the equatorial plane. the two-components, disk and halo, are disaggregated out of the halo component and oscillate steadily. our results are able to explain multiple observational features: 1. the presence of qpo/peaked noise in the hecto-hz range; 2. low-frequency qpo and its harmonic; 3. high-frequency khz qpos and changes in their centroid frequencies. the pds of the inviscid cases show features found in observation, especially the hmxbs such as cir x-1. we also explore the more general cases with viscosity and cooling to compare those results with observation. | what is the origin of qpos in accreting neutron stars? |
a model and algorithm for the cooling of the magnetized neutron stars are presented. the cooling evolution described by a system of parabolic partial differential equations with non-linear coeffcients is solved using the alternating direction implicit method. a difference scheme and the preliminary results of simulations are presented. | an algorithm for the simulation of the magnetized neutron star cooling |
possible mechanisms of creation of both hyperheavy nuclei by electron-nuclear collapse and neutron matter by condensation of ultracold neutrons are discussed. the fundamental possibility of the existence of such objects was previously substantiated by a.b.migdal, who suggested that the known set of proton-neutron nuclei with mass numbers from 0 to 300 and a maximum specific binding energy of about 8 mev / nucleon at a≍60 corresponds to the first region, beyond which (starting from about the charge z ≍ (hc/e2)3/2≍1600) there is an additional region describing a possible state of nuclear matter, stabilized by a pion condensate. in this region, the maximum specific energy corresponds to ≍15 mev / nucleon at a ≍ 100000. it is shown that neutron matter can be obtained under certain conditions, and its systematization can be realized as an addition to the periodic table. when solving such problems, it becomes quite real to study not only physical, but also chemical, and possibly engineering and technical properties. analysis shows that the stability of neutron matter at the microlevel is ensured by the tamm interaction and the hund beta equilibrium. such matter can be quite stable not only on the mega-level (neutron stars) due to gravitational interaction, as was a priori assumed earlier, but also on the scale of "ordinary" matter. the process of neutronization is possible not only with critical gravitational interaction, but also by other mechanisms (supercritical increase in the atomic number of elements due to electron-nuclear collapse and condensation of ultracold neutrons), which opens the way to the fundamental possibility of obtaining both neutron matter in laboratory conditions and superheavy nuclei. based on the works of migdal, tamm and hund, the possibility of the existence of stable neutron matter (with z >> 175, n > > z, a> 103-105 and a size of 200-300 femtometers and more) is argued at the microlevel, and not only at the mega-level, as is now considered in astrophysics. a critical analysis of the well-established concept of the minimum possible mass of neutron stars is carried out. the following quantum technological approaches to the realization of ucn condensation are proposed: 1. slow isothermal compression; 2. refrigerator for dissolving helium-3 and helium-4; 3. use of a conical concentrator for ucn focusing (vysotskii cone); 4. magnetic trap; 5. additional ucn laser cooling. neutron matter is considered as a potential cosmological candidate for dark matter. one should take into account the possibility of the formation of fragments of neutron matter as dark matter (neutral, femto-, pico- and nanoscale, the cooling of relics makes it difficult to detect them by now) already at the initial origin of the universe, which is the dominant process. the observable part of the universe is formed by the residual part of protons, and then by decayed single neutrons and unstable fragments of neutron matter (with z> 175, n >> z, but a <103-105). | obtaining neurton matter and hyperheavy nuclei: possible quantum-technological instrumental approaches |
the historical gravitational wave detections of last years ushered in a new era for the study of massive binaries evolution. in high mass x-ray binaries, a transient albeit decisive phase preceding compact binaries, a compact accretor orbits a massive star and captures part of its intense stellar wind. from the stellar photosphere down to the vicinity of the compact object, the flow undergoes successive phases. our numerical simulations offer a comprehensive picture of the accretion process along this journey. we report new results on the impact of the wind micro-structure on the x-ray time variability and how the revised downwards wind speed implies a significantly different flow geometry than the one previously considered. for wind speeds of the order of the orbital speed or lower, accretion is significantly enhanced and provided cooling is accounted for, transient disc-like structures form beyond the neutron star magnetosphere, with dramatic consequences on the torques applied to the compact object. the recent observational reports on the limited extent of the accretion disc in cygnus x-1 suggest that the disc is produced by this mechanism rather than a roche lobe overflow of the companion star. in vela x-1, such a structure remains to be observed but its indirect signatures through jets or the torques it applies on the neutron star could well be within our observational grasp. this accretion regime could also account for large mass transfer rates, up to levels suitable for ultra-luminous x-ray sources, without roche lobe overflow of the donor star, a situation observed in m101 ulx-1. | enhanced accretion and wind-captured discs in high mass x-ray binaries |
through the relativistic mean field theory and relevant weakinteractional cooling theories, the relativistic cooling properties inconventional and hyperonic neutron star matter are studied. also a comparison betweenrelativistic and non-relativistic results with the consideration of the gravity correction is performed.results show that the correction of relativistic effect in neutrino emission makes theneutrino emissivity, neutrino luminosity, and cooling rate be lower, in comparison with the non-relativistic case. due to the correction of relativistic effect in neutrino emission, the cooling rate of neutron star has the largest decline, for the conventional neutron star matter with the consideration of gravity correction. the rate of decline reaches 56% for the conventional neutron star with a mass of two solar masses, however, the decline in hyperonic matter is the smallest, about 38%. | relativistic correction on neutrino emission from neutron stars |
considering the octet baryons in relativistic mean field (rmf) theory, the entropy per baryon is selected to be 1 or 2. we investigate the influence of the entropy per baryon for the massive protoneutron star corresponding to psr j0348+0432. one set of coupling constants gl85 in rmf are selected to reproduce the mass of psr j0348+0432 at zero temperature, and then extended to describe the massive protoneutron stars with the per baryon entropy s=1 or s=2. it is found that the massive protoneutron stars have more hyperons than the cold neutron stars, the temperature increases with the increase of the density from surface to interior, and the existence of hyperons leads to the decrease of the interior temperature. entropy causes the increase of the mass of massive protoneutron star, and this effect is more obvious than that of the decreasing mass due to hyperons. the entropy per baryon brings on the increase of the radius of protoneutron star. in other words, the protoneutron star's cooling may be a contracting process. | composition and structure of massive protoneutron star psr j0348+0432 |
one of the key aspects in the comprehension of neutron star (ns) interiors is the identification of observables that may impose constraints on the equation of state (eos). at present, limits are obtained mainly through the study of the mass-radius relationship, the maximum rotational frequency and the cooling behaviour. however, since gravitational wave (gw) observatories such as advanced ligo and advanced virgo will open a new window of the observation of nss in the very near future, identifying observables that may emerge from the analysis of the gw emission of nss is crucial. to this end, we investigate non-radial oscillations of hadronic, hybrid and pure self-bound strange quark stars with maximum masses above the mass of the recently observed massive pulsars psr j1614-2230 and psr j0348-0432 with m ≈ 2 m⊙. we find that the first pressure mode for strange quark stars has a very different shape than for hadronic and hybrid stars. for strange quarks stars, the frequency of the p1 mode is larger than 7 khz and diverges at small stellar masses, but for hadronic and hybrid stars it is in the range 4-7 khz. this allows an observational identification of strange stars even if extra information such as the mass, the radius or the gravitational redshift of the object is unavailable or uncertain. also, we find as in previous works that the frequency of the g-mode associated with the quark-hadron discontinuity in a hybrid star is in the range 0.4-1 khz for all masses. thus, compact objects emitting gws above 7 khz should be interpreted as strange quark stars, and those emitting a signal within 0.4-1 khz should be interpreted as hybrid stars. | toward linking fluid pulsation modes to the internal composition of neutron stars |
neutron stars in low mass x-ray binaries accrete enough mass over their lifetimes to replace their entire crust. the accreted matter undergoes a series of nuclear reactions in the crust as it is compressed by continued accretion to higher density. these reactions, which include electron captures, neutron emissions, and pycnonuclear reactions, heat the crust and core of the neutron star. in this talk i will discuss what we can learn from observations of transiently accreting neutron stars in quiescence, when accretion has turned off and we can see emission from the neutron star directly. the quiescent luminosity of these neutron stars constrains the neutrino emissivity in the neutron star core. in systems with long accretion outbursts, observations of thermal relaxation of the crust in quiescence enable, for the first time, constraints on the thermal conductivity and heat capacity of the crust. in this way, low mass x-ray binary neutron stars offer a remarkable chance to constrain the properties of dense neutron-rich matter, such as neutron superfluidity and pasta phases in the inner crust of neutron stars. | heating and cooling in accreting neutron stars |
precise measurement of the mass-radius relation of a neutron star (ns) is crucial to determine the equation of state of the ultra dense matter. instead of directly measuring the mass and radius, it is often measured the mass-radius ratio, i.e. gravitational redshift at the ns surface, as it is free from the uncertainty to the source distance. if we can detect spectral features in the emission from the ns photosphere, which may be observable during the thermonuclear x-ray bursts, we can directly measure the gravitational redshift. thus, we are systematically analyzing the suzaku archival data looking for the thermonuclear x-ray bursts.grs 1747-312 is a type i x-ray burst source located in the globular cluster terzan 6. it was observed with suzaku as a part of galactic bulge mapping observations in september, 2009, for a total exposure of 45.3 ks. an exceptionally large x-ray burst with photospheric radius expansion was detected during the observation. the burst duration exceeded an hour. unfortunately, most of the decay of the burst was not observed due to the satellite passage through the south atlantic anomaly.we detected a broad feature in the energy spectrum of the burst above 7 kev in its cooling phase. the feature resembled that of an absorption edge, but was significantly smeared. we found that it was best reproduced by a rotation-broadened absorption edge, where the photo-electric absorption edge was smeared by the rapid spin of the ns. the smeared edge may be produced by the dominant products of the x-ray burst, i.e. hydrogen-like fe (9.28 kev) or ni (10.78 kev). if this identification is correct, the gravitational red shift would be 1.30+-0.02 or 1.51+-0.02, respectively, corresponding to the ns radius of 10.1+-0.3 or 7.4+-0.1 km, for an assumed ns mass of 1.4 solar mass. because the absorption edge is not completely smeared out even with the rapid spin of the ns, this can be a powerful tool to measure the gravitational redshift of the nss. | a broad spectral feature detected during the cooling phase of a thermonuclear x-ray burst from grs 1747-312 with suzaku |
studying thermal evolution of neutron stars (nss) is one of a few ways to investigate the properties of superdense matter in their cores. we study the cooling of isolated nss (inss) and deep crustal heating of transiently accreting nss in x-ray transients (xrts, binary systems with low-mass companions). currently, nearly 50 of such nss are observed, and one can apply statistical methods to analyze the whole dataset. we propose a method for such analysis based on thermal evolution theory for individual stars and on averaging the results over ns mass distributions. we calculate the distributions of inss and accreting nss (anss) in xrts over cooling and heating diagrams respectively. comparing theoretical and observational distributions one can infer information on physical properties of superdense matter and on mass distributions of inss and anss. | statistical approach to thermal evolution of neutron stars |
in this work, we investigate the properties of hybrid stars based on the togashi eos with a low value for the symmetry energy. we adopt the togashi eos and (2 + 1) - flavor njl eos to describe the hadron matter and quark matter, respectively, and construct the hybrid star with the 3-window interpolation approach. the structure of the hybrid star satisfies the observational constraints well, and its mass-radius relation is similar to that of the pure neutron star for the togashi eos which the maximum mass exceeds 2 times of solar mass and the radius is small due to a low symmetry energy. it is consistent with the current constraints on the mass-radius from the observational data. we also study the cooling simulation of neutron stars in this paper. comparing the cooling curves with observations, our investigation shows that the cooling curves of hybrid stars are compatible with most of the pulsar's data. | the properties of hybrid stars in a low symmetry energy model |
in this talk, i will present our recent work on a new mechanism for deep crustal heating in accreting neutron stars. during active accretion, charged pions (π+) are produced in nuclear collisions on the neutron star surface. upon decay, they provide a flux of neutrinos into the neutron star crust. we find that for massive and/or compact neutron stars, neutrinos deposit ~ 1-- 2 mev of heat per accreted nucleon into the inner crust. the strength of neutrino heating is comparable to the previously known sources of deep crustal heating, such as from pycnonuclear fusion reactions, and is relevant for studies of cooling neutron stars. we model the thermal evolution of a transient neutron star in a low-mass x-ray binary, and in the particular case of the neutron star mxb 1659-29, we show that additional deep crustal heating requires a higher thermal conductivity for the neutron star inner crust. a better knowledge of pion production cross sections near the threshold would improve the accuracy of our predictions. | deep crustal heating and neutron star cooling observation |
pulsars are stars from which electromagnetic radiation is observed to pulsate in well-defined time intervals as the star rotates and the emission of eletromagnetic signal is located in a place different from the rotation center. the frequencies of the pulses decay with time, quantified by the braking index (n). in the canonical model n = 3, in general, for all pulsars, but observational data shows that n is lower than 3. in this work a new model is presented, based on a modification of the canonical one incorporating the influence of neutron and proton density that appear in the superfluid core and, as the star cools down, the density of the superfluid core increases making the star to shrink with time and temperature, making the inertia moment to decrease. the difference ot this model from the canonical one is that the star moment of inertia decreases with time (what would accelerate the rotation of the star) what makes the star to not slow down as fast as it should without this process. | the influence of superfluid core cooling in the braking index of pulsars. |
<strong>symbiotic stars are interacting binaries</strong> consisting of an evolved, <strong>cool giant</strong> that is transferring mass to a hot companion - a <strong>white dwarf</strong> or rarely a neutron star. the presence of both ionized and neutral regions in their surroundings, interacting winds, jets, accretion disks, or dust forming regions make them <strong>extraordinary astrophysical laboratories</strong> for studying various aspects of interaction and evolution in binary systems. although recent surveys discovered several dozens of new symbiotic variables, their careful analysis and deriving the parameters of the components of these systems are needed in order to understand the mechanisms of their <strong>interactions and evolution</strong>. our <strong>new online database of symbiotic variables</strong> can serve as a basis for statistical studies of the characteristics of the symbiotic population. as presented in this contribution, gaia observations made public in the<strong> gaia edr3 </strong>and impatiently awaited in subsequent releases could be <strong>very suitable for this purpose </strong>considering the gaia satellite can provide data obtained uniformly for the entire sample. | characterizing cool giants in symbiotic binaries using the gaia edr3 data |
type i x-ray bursts are thermonuclear flashes observed from the surfaces of accreting neutron stars in low mass x-ray binaries. oscillations have been observed during the rise and/or decay of some of these x-ray bursts. those seen during the rise can be well explained by a spreading hot spot model, but large amplitude oscillations in the decay phase remain mysterious because of the absence of a clear-cut source of asymmetry. here we present the results of our computations of the light curves and amplitudes of oscillations in x-ray burst models that realistically account for both flame spreading and subsequent cooling. for the cooling phase of the burst we use two simple phenomenological models. the first considers asymmetric cooling that can achieve high amplitudes in the tail. the second considers a sustained temperature pattern on the stellar surface that is produced by r-modes propagating in the surface fluid ocean of the star. we will present some simulated burst light curves/spectra using these models and nicer response files, and will show the capabilities of nicer to detect and study burst oscillations. nicer will enable us to study burst oscillations in the energy band below ~3 kev, where there has been no previous measurements of these phenomena. | burst oscillation studies with nicer |
we propose the first observational study of the thermal evolution of old neutron stars (nss) through far-uv observations of three nearby pulsars in the age range from 17 myr to 6 gyr. the cooling history of younger nss is being mapped out in the x-rays, providing important information on the properties of the super-dense matter in the ns interiors. however, only one old ns, millisecond psr j0437-4715, has so far revealed its thermal emission, which has been detected with hst in the far-uv. the observed high temperature of about 1.5*10^5 k unavoidably requires a heating mechanism to operate in the old ns interiors. two possible heating mechanisms have been identified, but their relative importance and parameters, which depend on poorly understood properties of the ns matter, are currently unclear. the proposed program will discriminate between the competing heating models and help constrain the properties of matter under extreme physical conditions, such as neutron and proton superfluidity and frictional forces between the superfluid vortices and the crustal solid. observations of the far-uv surface emission of old nss, undetectable from the ground, is the only way to establish their long-term thermal evolution (cooling curves) and so probe the cooling/heating mechanisms and the properties of matter at super-high densities. therefore, the uv capabilities of the hst offer a unique opportunity to carry out such a study, which will be a long-lasting legacy of hst. | thermal evolution of old neutron stars |
binary star systems composed of two white dwarfs are a natural outcome of stellar evolution. angular momentum losses from gravitational wave radiation cause the binary system's orbit to shrink until the two white dwarfs merge. the final outcome of the merger depends on the masses of the white dwarfs. some potential outcomes, such as supernova explosions, may occur during or soon after the merger. other outcomes, which i will refer to as "long-term" outcomes, occur as the merger remnant cools and its structure adjusts to the new state created during the energetic merger.in my dissertation, i quantitatively explore the long-term outcomes of the mergers of two white dwarfs. i focus primarily on the formation of neutron stars via accretion-induced collapse and the formation of two types of unusual stars, the single sub-dwarf b stars (hot, core helium fusing stars) and the r coronae borealis stars (cool, carbon-rich giant stars). beginning with the results from my previous simulations of the short-lived viscous disk initially present in these remnants, i use the state-of-the-art mesa stellar evolution code to follow their thermal evolution.this work improves the quantitative understanding of which white dwarf binaries lead to a particular outcome and better characterizes the observational signatures of these outcomes. for systems that will undergo accretion-induced collapse, these simulations yield improved progenitor models that can then be used to explore the collapse and formation of a neutron star. | the long-term outcomes of double white dwarf mergers |
the possible presence of amorphous and heterogeneous phases in the inner crust of a neutron star is expected to reduce the electrical conductivity of the crust, with potentially important consequences on the magneto-thermal evolution of the star. in cooling simulations, the disorder is quantified by an impurity parameter which is often taken as a free parameter. we aim to give a quantitative prediction of the impurity parameter as a function of the density in the crust,performing microscopic calculations including up-to-date microphysics of the crust. a multi-component approach is developed at finite temperature using a compressible liquid drop description of the ions with an improved energy functional based on recent microscopic nuclear models and optimized on extended thomas-fermi calculations. thermodynamic consistency is ensured by adding a rearrangement term and deviations from the linear mixing rule are included in the liquid phase. the impurity parameter is consistently calculated at the crystallization temperature as determined in the one-component plasma approximation for the different functionals. our calculations show that at the crystallization temperature the composition of the inner crust is dominated by nuclei with charge number around $z \approx 40$, while the range of the $z$ distribution varies from about 20 near the neutron drip to about 40 closer to the crust-core transition. this reflects on the behavior of the impurity parameter that monotonically increases with density up to around 40 in the deeper regions of the inner crust. our study shows that the contribution of impurities is non-negligible, thus potentially having an impact on the transport properties in the neutron-star crust. the obtained values of the impurity parameter represent a lower limit; larger values are expected in the presence of non-spherical geometries and/or fast cooling dynamics. | inner crust of a neutron star at the point of crystallization in a multicomponent approach (corrigendum) |
in neutron stars the nuclear asymmetric matter is expected to undergo phase transitions to a superfluid state. according to simple estimates, neutron matter in the inner crust and just below should be in the s-wave superfluid phase, corresponding to the neutron-neutron 1s0 channel. at higher density in the core also the proton component should be superfluid, while in the inner core the neutron matter can be in the 3p2 superfluid phase. superluidity is believed to be at the basis of the glitches phenomenon and to play a decisive influence on many processes like transport, neutrino emission and cooling, and so on. one of the peculiarity of the superfluid phase is the presence of characteristic collective excitation, the so called 'phonons', that correspond to smooth modulations of the order parameter and display a linear spectrum at low enough momentum. this paper is a brief review of the different phonons that can appear in neutron star superfuid matter and their role in several dynamical processes. particular emphasis is put on the spectral functions of the different components, that is neutron, protons and electrons, which reveal their mutual influence. the open problems are discussed and indications on the work that remain to be done are given. | superfluid phonons in neutron star core |
low mass x-ray binaries are star systems in which a neutron star or a small black hole is paired with a companion star with mass comparable to that of the sun. during accretion, the companion star donates matter to the compact object in the system and increases its temperature. when accretion ends, a stage called quiescence, the compact object begins to cool as it moves back toward thermal equilibrium. properties of various neutron stars' crusts can be modeled based on how long the stars take to return to thermal equilibrium. previous research demonstrated an inverse-square relationship between the impurity of neutron star crust and the radius of the star. 100 combinations of possible radii, crust pressures, star masses, and maximum possible mass before black hole collapse were generated by an equation of state (eos) and were used to arrive at the previously mentioned conclusion. current research focuses on demonstrating a more in-depth relationship between the neutron star radius and crustal impurity by using 4000 combinations of generated parameters created by multiple eoss. | digging deeper into the properties of a cooling neutron star's crust |
neutron stars are unique natural laboratories to study bulk nuclear matter. our understanding of these dense stars has been driven by x-ray and gamma-ray observatories; by the detection of gravitational waves; and by ground-breaking nuclear physics experiments and the coming facility for rare isotope beams. for low-mass xray binaries, in which the neutron star accretes hydrogen- or helium-rich material, x-ray observations of accretion-induced phenomena over timescales ranging from seconds to decades provide important information about different layers of the neutron star. during accretion, runaway thermonuclear burning of the accreted material is observable as a type i x-ray burst. compression of the underlying crust by accretion induces reactions that heat the crust; for transiently accreting systems, the observed cooling of the crust when accretion halts provides vital information about the interior state of the neutron star. despite recent successes in modeling the interior of neutron stars, there remain challenges to our understanding: the rapid cooling of transients immediately following an outburst implies that much of the heating in the crust is unaccounted for; further, the high inferred thermal conductivity implies that the deep crust has a locally pure composition, although it is built from a broad distribution of isotopes; finally there remains the open question of whether asymmetrical burning over the neutron star surface could eventually lead to a sizeable mass quadrupole that would be potentially detectable from steady gravitational wave emission. we propose to address these challenges. we shall explore how a delayed response between the heating rate in the crust and the accretion rate affects the interpretation of the cooling lightcurves; whether the separation of matter into locally pure domains can remain in equilibrium; and how the diffusion of neutrons might eradicate horizontal gradients in composition in the inner crust, and hence limit the mass quadrupole. finally, we shall explore whether asymmetries in the surface nuclear burning can lead to asymmetries in the heating and thermal conducivity of the crust, and whether these crust asymmetries can in turn feed back on the surface burning and surface modes. | the complex geology of a neutron star's crust |
we propose a 72 ks epic observation of the recently identified youngpulsar psr j0837-2454. the resulting first-time x-ray spectrum and deepimage of the pulsar, complemented by proposed radio observations, willdetermine whether this pulsar is the first known product of a runawayo/b progenitor star or is a massive neutron star that has been cooled bythe fast direct urca process to become one of the coldest young neutronstars known. xmm-newton affords the necessary sensitivity and timeresolution to measure the spectrum of this faint pulsar and potentiallyits x-ray pulse profile. | x-ray properties of the unique runaway or very cool neutron star psr j0837-2454 |
the origin of half of the elements heavier than iron- the so-called r-process elements including gold and uranium, is a central unsolved mystery in astrophysics. recent observations utilising light and gravitational waves have demonstrated that at least some of these elements are formed through the merger of two neutron stars, but such a population struggles to reproduce the enrichment seen early in the lives of some of the oldest, lowest metallicity stars. instead, recent work implies that the accretion discs formed in the stellar collapse that powers a long duration gamma-ray burst could in-fact be a dominant site. the signature of their creation is a late time infrared component visible on top of the associated supernova light. the extreme opacities of some elements mean this could peak in the mid-ir, and it is at these wavelengths that the contrast between a cool r-process dominated component and a hotter, 'normal' supernova is at its largest. we propose to search for this component with spitzer observations of the recently detected, local (z=0.08) long grb 190829a (supported by approved optical/nir observations with the vlt and hst). these observations provide the first and only opportunity for spitzer to test if collapsars create very heavy elements. | do collapsars create the heaviest elements? |
following a neutron star merger, neutrinos are the primary means of cooling the resulting accretion disk and remnant compact object, they drive outflows, and they determine the abundances of elements formed in the ejecta. state-of-the-art numerical relativity simulations of these mergers employ a variety of methods for accounting for this radiation transport at differing levels of cost, complexity, and accuracy. i will briefly justify the local interaction approximation that is the basis for all current methods, describe the place each class of methods has in current science goals, and divine the future needs of relativistic radiation transport. furthermore, i will introduce current efforts to understand the effects of the quantum nature of neutrino flavor and spin, including numerical methods, microscopic instabilities, and attempts at parameterizing sub-grid models of neutrino flavor transformation for inclusion in global numerical relativity simulations. | neutrino kinetics in neutron star mergers |
observations of quasi-persistent x-ray transients yield valuable constraints for neutron star physics and structure. the nuclear reactions which occur during the outburst phase determine the composition of the neutron star crust. during the cooling phase, observations probe the thermal structure of the curst. nuclear reactions such as electron capture and beta decay cycling (urca cycling) can cool the neutron star, impacting such observations, and may also affect the behavior of x-ray bursts. a thorough understanding of these reactions is therefore necessary for correct interpretation of x-ray observations of x-ray bursts, superbursts, and crustal cooling. the yet- unknown contribution of urca cooling to the overall cooling of the neutron star depends both on the abundance of potential coolers (the ash composition) as well as the ground state to ground state transition strengths between the urca pairs. this work will detail a new dedicated experimental program of measurements of ground state beta-decay strengths in potential crust urca coolers at the national superconducting cyclotron laboratory (nscl), present first results, and discuss the impact on neutron star cooling. this work was performed under the auspices of the u.s. department of energy by lawrence livermore national laboratory under contract de-ac52-07na27344 and supported by ldrd 019-er-36. this work was conducted with the support of michigan state university, the national science foundation under grants phy-1102511, phy- 1404442, phy-1713857, phy-1430152 (jina center for the evolution of the elements), and ast-1516969. | production and impact of urca nuclides |
we propose a chandra+swift too program to observe cooling of the neutron star crust in a transiently accreting system, with the aim of probing the behavior and properties of ultra-dense matter. after the crust is heated during an outburst by a variety of nuclear reactions, it will cool down in quiescence until thermal equilibrium with the core is reached. following this cooling process in several systems has already provided important new insights into the structure of neutron stars, but question remain. expanding the current source sample is key to increasing our understanding of the accretion-induced heating processes in neutron star crusts. our multi-cycle program combines the strengths of chandra and swift and is optimized to achieve our goals. | crustal cooling in accretion-heated neutron stars |
passively cooling neutron stars are expected to reach undetectably low surface temperatures $t_s < 10^{4}$ k within less than $10^7$ yr. however, likely thermal ultraviolet emission was detected from the gyr-old millisecond pulsars psr j0437$-$4715 and psr j2124$-$3358 and the $\sim$ $10^7$ yr-old classical pulsar b0950$+$08, implying temperatures $t_s \sim 10^5$ k. this discrepancy could be explained by various heating mechanisms proposed in the literature. here, we computed thermal evolution curves considering different heating mechanisms, contrasting them with the observations. we found that either rotochemical heating with modified urca reactions in the core, pycnonuclear reactions in the deep layers of the crust, or the heat released by the friction of superfluid vortices could maintain the neutron stars hot enough beyond the standard cooling time to match the observations, while at the same time being consistent with the low upper limit found for psr j2144$-$3943. even when these mechanisms are combined, the predicted temperatures are compatible with the observed ones. | contrasting neutron star heating mechanisms with hubble space telescope observations |
the aim of this slow too proposal is to monitor the next be/x-ray transient and increasing the number of high-magnetic field nss in the small sample to obtain high-quality post-outburst spectra, which hold the key to understanding the physical differences in cooling among nss. for this, the high signal-to-noise and remarkable accuracy of chandra are required to study be/x-ray transients at low x-ray luminosities. the new observations will provide key data to i) better constrain the temporal evolution of the crust temperature in highly magnetized accreting nss, and ii) use the observed cooling curves as input into our 2d crust cooling models incorporating magnetic fields. this is required to understand the role of such magnetic fields on the crust heating/cooling scenario of accreting nss | cooling emission from highly magnetized neutron-star crusts |
risk assessments are fundamental to invasive species management and are underpinned by comprehensive characterization of invasive species impacts. our understanding of the impacts of invasive species is growing constantly, and several recently developed frameworks offer the opportunity to systematically categorize environmental and socioeconomic impacts of invasive species. invasive ants are among the most widespread and damaging invaders. although a handful of species receives most of the policy attention, nearly 200 species have established outside their native range. here, we provide a global, comprehensive assessment of the impacts of ants and propose a priority list of risk species. we used the socioeconomic impact classification for alien taxa (seicat), environmental impact classification for alien taxa (eicat) and generic impact scoring system (giss) to analyze 642 unique sources for 100 named species. different methodologies provided generally consistent results. the most frequently identified socioeconomic impacts were to human health. environmental impacts were primarily on animal and plant populations, with the most common mechanisms being predation and competition. species recognized as harmful nearly 20 years ago featured prominently, including wasmannia auropunctata (little fire ant, electric ant), solenopsis invicta (red imported fire ant), anoplolepis gracilipes (yellow crazy ant), and pheidole megacephala (african big‑headed ant). all these species except w. auropunctata have been implicated in local extinctions of native species. although our assessments affirmed that the most serious impacts have been driven by a small number of species, our results also highlighted a substantial number of less well publicized species that have had major environmental impacts and may currently be overlooked when prioritizing prevention efforts. several of these species were ranked as high or higher than some of the previously recognized "usual suspects," most notably nylanderia fulva (tawny crazy ant). we compared and combined our assessments with trait‑based profiles and other lists to propose a consensus set of 31 priority species. ever‑increasing global trade contributes to growing rates of species introductions. the integrated approaches we used can contribute to robust, holistic risk assessments for many taxa entrained in these pathways. | a global review of socioeconomic and environmental impacts of ants reveals new insights for risk assessment |
we present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. our simulation tools have recently been improved to incorporate the effects of neutrino cooling and have been generalized to allow for tabular equations of state to describe the degenerate matter. of particular interest are possible electromagnetic counterparts to the gravitational radiation that emerges from these systems. we focus on magnetospheric interactions that ultimately tap into the gravitational potential energy of the binary to power a poynting flux and deposition of energy through joule heating and magnetic reconnection. we gratefully acknowledge the support of nasa through the astrophysics theory program grant nnx13ah01g. | coalescence of magnetized binary neutron star systems |
we analyze broadband x-ray data of ngc 6946 x-1 and probe plausible accretion scenarios in this ulx. ngc 6946 x-1 is a persistent soft source with broadband continuum spectra described by two thermal disk components. the cool accretion disk temperature t cool ~ 0.2 kev and the presence of a ~0.9 kev emission/absorption broad feature suggest evidence of an optically thick wind due to supercritical accretion. the hot geometrically modified accretion disk has an inner temperature of t hot ~ 2 kev with a radially dependent profile t(r) ∝ r -0.5, expected in a slim-disk scenario. further, the measurement based on a realistic inclination angle of the disk indicates that the mass of the host compact object is comparable to a ~6-10 m ⊙ nonrotating black hole or the system hosts a moderately magnetized neutron star with a b ≲ 2 × 1011 g magnetic field. overall, the detected spectral curvature, high luminosity, flux contribution from two thermal disk components, and estimated accretion rate support the super-eddington accretion scenario. | constraint on the accretion of ngc 6946 x-1 using broadband x-ray data |
colibrì is canada's flagship x-ray observatory, proposed to have multiple aperture x-ray optics with cryogenically cooled transition-edge detectors for achieving high-energy and high-time resolution, as well as high throughput and sensitivity in the 0.1-15 kev range. these specifications are tuned to capture the evolving spectral signatures of the bright accretion flows of black holes and neutron stars, and probe outflows on all scales along the line-of-sight. we will highlight exciting case studies that illustrate the promise of colibrì to fill a focussed niche within the cohort of future proposed x-ray missions. | black hole astrophysics with colibrì |
neutron star provides unique environments for the investigation of the physics of extreme dense matter beyond normal nuclear saturation density. in such high density environments, hadrons with strange quarks are expected to play very important role in stabilizing the system. kaons and hyperons are the lowest mass states with strangeness among meson and bayron families, respectively. in this work, we investigate the role of kaons and hyperons to the neutron star mass, and discuss their role in the neutron star cooling. | role of strangeness to the neutron star mass and cooling |
crustal cooling of accretion-heated neutron stars provides insight into the stellar interior of neutron stars. the neutron star x-ray transient, ks 1731-260, was in outburst for 12.5 years before returning to quiescence in 2001. we have monitored the cooling of this source since then through chandra and xmm-newton observations. here, we present a 150 ks chandra observation of ks 1731-260 taken in august 2015, about 14.5 years into quiescence, and 6 years after the previous observation. we find that the neutron star surface temperature is consistent with the previous observation, suggesting that crustal cooling has likely stopped and the crust has reached thermal equilibrium with the core. using a theoretical crust thermal evolution code, we fit the observed cooling curves and constrain the core temperature (t_c = 9.35±0.25×10^7 k), composition (q_{imp} = 4.4^{+2.2}_{-0.5}) and level of extra shallow heating required (q_{sh} = 1.36±0.18 mev/nucleon). we find that the presence of a low thermal conductivity layer, as expected from nuclear pasta, is not required to fit the cooling curve well, but cannot be excluded either. | the thermal state of ks 1731-260 after 14.5 years in quiescence |
the objective of this proposal is to pioneer a new computational tool, the lattice boltzmann method, for simulating condensed nuclear matter in the neutron star inner crust. this will be used to study the properties of the nuclear "pasta" phases, predicted to exist at the crust-core interface, over significantly larger volumes than the current stateof-the-art calculations. the lattice boltzmann method has been used extensively to study soft condensed matter materials on earth; this will be the first time it has been applied to study a nuclear astromaterial, and will result in more robust physical predictions for the material properties of the deep layers of the neutron star crust. x-ray observations of a number of neutron star phenomena may bear the imprint of the mechanical and transport properties of these exotic phases, and nasa's recently-launched neutron star interior composition explorer (nicer) has a stated aim of measuring those properties in the crust. the project has the following specific goals: 1. implement, for the first time, the lattice boltzmann computational method to simulate a complex nuclear fluid under the physical conditions manifest at the base of a neutron star crust, and the first 2d and 3d mesoscopic simulations of nuclear pasta there. implementation and validation of the code will be conducted by comparing the resulting phenomenology with the results of simulations of analogous terrestrial soft matter simulations using the lb method, as well as existing classical molecular dynamics and quantum mechanical simulations of nuclear pasta. 2. conduct the first mesoscale calculations of the shear modulus, breaking strain, viscosity, and thermal and electrical conductivities of nuclear pasta under neutron star crust conditions, with and without strong crustal magnetic fields. such calculations will, for the first time, self-consistently account for the affect of disorder arising from coexisting phases and defects in the pasta structures simultaneously. the dependence on the nuclear equation of state will be selfconsistently examined, and the mechanical and transport properties published alongside their respective equations of state for self-consistent incorporation into astrophysical simulations. this will result in more robust and physically grounded predictions for a number of observables. 3. evaluate the effects of the newly calculated mechanical and transport properties on the following astrophysical observables of particular relevance to nasa's past, current and future x-ray and gravitational-wave observatories: (i) the frequency of quasi-periodic oscillations in the crust of highly magnetized neutron stars, potentially observable in the x-ray tails of gamma-ray flares (ii) the frequency and damping of rotationally-excited r-modes, potentially observable as modulations in the x-ray light curves of quiescent neutron stars and indirectly in the spin-distribution of recycled x-ray pulsars; (iii) the crust-cooling timescale, probed by x-ray measurements of accreting neutron stars in quiescence, and (iv) the maximum size of mountains supported by the crust, potentially observable in the resulting persistent gravitational wave signal. 4. explore future astrophysical applications of the lattice boltzmann method. particularly, the use of the lattice boltzmann method to simulate superfluid flow and the motion of vortices in the pasta phases, of high importance to the modeling and interpretation of pulsar glitches, will be examined. | lattice boltzmann simulations of soft nuclear astromaterials in neutron star crusts |
a quantitative analysis of luminosity and temperature observations from isolated neutron stars constrains two nucleon superfluid critical temperatures: the neutron triplet superfluid critical temperature and the proton singlet superconducting critical temperature. the neutron star observations imply that the most likely value for the neutron triplet critical temperature is 2 .09-1 . 41 + 4 . 37 ×108 k, while the most likely value for the proton singlet critical temperature is 7 .59-5 . 81 + 2 . 48 ×109 k. our results assumed minimal cooling, and these results are only valid when vela is removed from our data set. the inclusion of vela increased the gaps significantly, as vela has a very low temperature for its young age. we present preliminary results which include enhanced cooling and variations of the neutron star masses and equation of state parameters. these preliminary results show that vela is likely more massive and has a direct urca cooling process which explains its low temperature. nsf phy 1554876. | constraining superfluidity in dense matter from the cooling of isolated neutron stars |
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