47 research outputs found
Statistical theory of thermal evolution of neutron stars
Thermal evolution of neutron stars is known to depend on the properties of
superdense matter in neutron star cores. We suggest a statistical analysis of
isolated cooling middle-aged neutron stars and old transiently accreting
quasi-stationary neutron stars warmed up by deep crustal heating in low-mass
X-ray binaries. The method is based on simulations of the evolution of stars of
different masses and on averaging the results over respective mass
distributions. This gives theoretical distributions of isolated neutron stars
in the surface temperature--age plane and of accreting stars in the photon
thermal luminosity--mean mass accretion rate plane to be compared with
observations. This approach permits to explore not only superdense matter but
also the mass distributions of isolated and accreting neutron stars. We show
that the observations of these stars can be reasonably well explained by
assuming the presence of the powerful direct Urca process of neutrino emission
in the inner cores of massive stars, introducing a slight broadening of the
direct Urca threshold (for instance, by proton superfluidity), and by tuning
mass distributions of isolated and accreted neutron stars.Comment: 13 pages, 20 figure
Bayesian Inference of the Dense Matter Equation of State built upon Covariant Density Functionals
A modified version of the density dependent covariant density functional
model proposed in [T. Malik, M. Ferreira, B. K. Agrawal and C. Provid\^encia,
ApJ 930, 17 (2022)] is employed in a Bayesian analysis to determine the
equation of state (EOS) of dense matter with nucleonic degrees of freedom.
Various constraints from nuclear physics and microscopic calculations of pure
neutron matter (PNM) along with a lower bound on the maximum mass of neutron
stars (NSs) are imposed on the EOS models to investigate the effectiveness of
progressive incorporation of the constraints, their compatibility as well as
correlations among parameters of nuclear matter and properties of NSs. Our
results include the different roles played by pressure and energy per particle
of PNM in constraining the isovector behavior of nuclear matter; tension with
the values of Dirac effective mass extracted from spin-orbit splitting;
correlations between the radius of the canonical mass NS and second and third
order coefficients in the Taylor expansion of energy per particle as a function
of density; correlation between the central pressure of the maximum mass
configuration and Dirac effective mass of the nucleon at saturation. For some
of our models the tail of the NS maximum mass reaches ,
which means that the secondary object in GW190814 could have been a NS.Comment: 22 pages, 11 figures, accepted to Phys. Rev.
NS 1987A in SN 1987A
The possible detection of a compact object in the remnant of SN 1987A
presents an unprecedented opportunity to follow its early evolution. The
suspected detection stems from an excess of infrared emission from a dust blob
near the compact object's predicted position. The infrared excess could be due
to the decay of isotopes like 44Ti, accretion luminosity from a neutron star or
black hole, magnetospheric emission or a wind originating from the spindown of
a pulsar, or thermal emission from an embedded, cooling neutron star (NS
1987A). It is shown that the last possibility is the most plausible as the
other explanations are disfavored by other observations and/or require
fine-tuning of parameters. Not only are there indications the dust blob
overlaps the predicted location of a kicked compact remnant, but its excess
luminosity also matches the expected thermal power of a 30 year old neutron
star. Furthermore, models of cooling neutron stars within the Minimal Cooling
paradigm readily fit both NS 1987A and Cas A, the next-youngest known neutron
star. If correct, a long heat transport timescale in the crust and a large
effective stellar temperature are favored, implying relatively limited crustal
n-1S0 superfluidity and an envelope with a thick layer of light elements,
respectively. If the locations don't overlap, then pulsar spindown or accretion
might be more likely, but the pulsar's period and magnetic field or the
accretion rate must be rather finely tuned. In this case, NS 1987A may have
enhanced cooling and/or a heavy-element envelope.Comment: 21 pages, 6 figures, to be published in Ap
Thermal evolution of neo-neutron stars. I: envelopes, Eddington luminosity phase and implications for GW170817
A neo-neutron star is a hot neutron star that has just become transparent to
neutrinos. In a core collapse supernova or accretion induced collapse of a
white dwarf the neo-neutron star phase directly follows the proto-neutron star
phase, about 30 to 60 seconds after the initial collapse. It will also be
present in a binary neutron star merger in the case the "born-again" hot
massive compact star does not immediately collapse into a black hole. Eddington
or even super-Eddington luminosities are present for some time. A neo-neutron
star produced in a core collapse supernova is not directly observable but the
one produced by a binary merger, likely associated with an off-axis short
gamma-ray burst, may be observable for some time as well as when produced in
the accretion induced collapse of a white dwarf. We present a first step in the
study of this neo-neutron star phase in a spherically symmetric configuration,
thus neglecting fast rotation, and also neglecting the effect of strong
magnetic fields. We put particular emphasis on determining how long the star
can sustain a near-Eddington luminosity and also show the importance of
positrons and contraction energy during neo-neutron star phase. We finally
discuss the observational prospects for neutron star mergers triggered by LIGO
and for accretion-induced collapse transients.Comment: 23 pages, 19 figures; accepted for publication in Ap
Frequencies of - and -oscillation modes in cold and hot compact stars
A large collection of equations of state (EOSs) built within the covariant
density functional (CDF) theory of hadronic matter and allowing for density
dependent (DD) couplings is employed to study polar - and - oscillations
of cold and hot compact stars. Correlations between oscillation frequencies of
cold purely nucleonic neutron stars (NSs), their global parameters as well as
properties of nuclear matter (NM) are investigated by considering a set of
models from Beznogov and Raduta, [Phys.~Rev.~C 107, 045803 (2023)], where a
number of constraints on the saturation properties of NM, pure neutron matter
(PNM) and the lower bound of the maximal NS mass were imposed within a Bayesian
framework. The roles of finite temperature and exotic particle degrees of
freedom, e.g., hyperons, -resonances, anti-kaon condensates or a hadron
to quark phase transition, are addressed by employing a family of models
publicly available on \textsc{CompOSE} and assuming idealized profiles of
temperature or entropy per baryon and charge fraction. We find that finite
temperature effects reduce the oscillation frequencies of nucleonic stars while
the opposite effect is obtained for stars with exotic particle degrees of
freedom. When the -law is employed to build finite temperature EOSs,
errors in estimating oscillation modes frequencies are of the order of 10\% to
30\%, depending on the mass. Throughout this work the Cowling approximation is
used.Comment: 12 pages, 7 figures, 2 table
Cooling of the Cassiopeia A neutron star and the effect of diffusive nuclear burning
The study of how neutron stars cool over time can provide invaluable insights
into fundamental physics such as the nuclear equation of state and
superconductivity and superfluidity. A critical relation in neutron star
cooling is the one between observed surface temperature and interior
temperature. This relation is determined by the composition of the neutron star
envelope and can be influenced by the process of diffusive nuclear burning
(DNB). We calculate models of envelopes that include DNB and find that DNB can
lead to a rapidly changing envelope composition which can be relevant for
understanding the long-term cooling behavior of neutron stars. We also report
on analysis of the latest temperature measurements of the young neutron star in
the Cassiopeia A supernova remnant. The 13 Chandra observations over 18 years
show that the neutron star's temperature is decreasing at a rate of 2-3 percent
per decade, and this rapid cooling can be explained by the presence of a proton
superconductor and neutron superfluid in the core of the star.Comment: 7 pages, 7 figures; to appear in the AIP Conference Proceedings of
the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the
Era of Gravitational Wave Astronomy (January 3-7, 2019, Xiamen, China