J. L. Zdunik

Nicolaus Copernicus Astronomical Center

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P. Haensel

Nicolaus Copernicus Astronomical Center

122

M. Bejger

Nicolaus Copernicus Astronomical Center

M. Fortin

Nicolaus Copernicus Astronomical Center

ÉG

Éric Gourgoulhon

Laboratoire Univers et Théories

D. Rosińska

Polish Academy of Sciences

N. Chamel

Université Libre de Bruxelles

A. F. Fantina

GANIL

T. Bulik

University of Warsaw

Lami Suleiman

Laboratoire Univers et Théories

D. Gondek

Nicolaus Copernicus Astronomical Center

Cooperative Institutions

National Institute for Astrophysics

233

University of Geneva

123

Swiss Institute of Comparative Law

117

Institute for Space Astrophysics and Planetology

117

University of Amsterdam

107

Consejo Superior de Investigaciones Científicas

SRON Netherlands Institute for Space Research

Centre National de la Recherche Scientifique

Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata

Technical University of Denmark

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Papers

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Rotating compact strange stars

arXiv (Cornell University) (2000)

D. Rosińska T. Bulik J. L. Zdunik Éric Gourgoulhon Saibal Ray

We compute numerical models of uniformly rotating strange stars (SS) in general relativity for the recently proposed QCD-based equation of state (EOS) of strange quark matter (Dey et al. 1998). Static models based on this EOS are characterised by a larger surface redshift than strange stars within the MIT bag model. The frequencies of the fastest rotating configurations described by Dey model are much higher than these for neutron stars (NS) and for the simplest SS MIT bag model. We determine a number of physical parameters for such stars and compare them with those obtained for NS. We construct constant baryon mass equilibrium sequences both normal and supramassive. Similarly to the NS a supramassive SS, prior to collapse to a black hole, spins up as it loses angular momentum. We find the upper limits on maximal masses and maximal frequencies of the rotating configurations. We show that the maximal rotating frequency for each of considered evolutionary sequences is never the Keplerian one. A normal and low mass supramassive strange stars gaining angular momentum always slows down just before reaching the Keplerian limit. For a high mass supramassive SS sequence the Keplerian configuration is the one with the lowest rotational frequency in the sequence. The value of $T/W$ for rapidly rotating SS of any mass is significantly higher than those for ordinary NS. For Keplerian configurations it increases as mass decreases. The results are robust for all linear self-bound equations of state.

Strange quark

Black hole (networking)

10.48550/arxiv.astro-ph/0007004

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Citations (4)

Heat blanketing envelopes vs cooling of neutron stars

Journal of Physics Conference Series (2017)

Mikhail V. Beznogov A. Y. Potekhin M. Fortin P. Haensel J. L. Zdunik

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.

Blanketing

Isothermal process

10.1088/1742-6596/932/1/012046

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Citations (1)

Neutron drip transition in accreting and nonaccreting neutron star crusts

Physical Review C (2015)

N. Chamel A. F. Fantina J. L. Zdunik P. Haensel

The neutron drip transition in the dense matter constituting the interior of neutron stars generally refers to the appearance of unbound neutrons as the matter density reaches some threshold density ${\ensuremath{\rho}}_{\mathrm{drip}}$. This transition has been mainly studied under the cold catalyzed matter hypothesis. However, this assumption is unrealistic for accreting neutron stars. After examining the physical processes that are thought to be allowed in both accreting and nonaccreting neutron stars, suitable conditions for the onset of neutron drip are derived and general analytical expressions for the neutron drip density and pressure are obtained. Moreover, we show that the neutron drip transition occurs at lower density and pressure than those predicted within the mean-nucleus approximation. This transition is studied numerically for various initial composition of the ashes from x-ray bursts and superbursts using microscopic nuclear mass models.

r-process

s-process

Dense matter

Nuclear drip line

10.1103/physrevc.91.055803

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Citations (54)

Rapid differential rotation of protoneutron stars and constraints on radio pulsars periods

Astronomy and Astrophysics (1998)

J. O. Goussard P. Haensel J. L. Zdunik

Models of differentially rotating protoneutron stars arecalculated,usingrealisticequationsofstateofdensehotmat- ter. Various conditions within the stellar interior, corresponding todifferentstagesofprotoneutronstarevolution,areconsidered. Numericalcalculationsareperformedwithintheapproximation of stationary equilibrium, using general relativistic equations of stationary motion of differentially rotating, axially symmetric stars and using a numerical code based on spectral methods. Families of differentially rotating models of a given baryon mass are calculated, using a two-parameter formula describ- ing the angular velocity prole within a rotating protoneutron star. Apart from the usual \mass shedding limit, we introduce an additional \minimal mass limit for differentially rotating protoneutron stars resulting from a type II supernovae. Max- imum angular momentum, which can be accommodated by a protoneutron star within these limits is calculated, for vari- ous thermal conditions in stellar interior, for a baryon mass of 1: 5M. In the case of a thermally homogeneous (isentropic or isothermal) neutrino-opaque interior this maximum angular momentum turns out to be somewhat higher than that of a cold neutron star of the same baryon mass, rotating uniformly at the mass shedding angular velocity. However, if the protoneutron star has a thermal structure characteristic of initial state, with a low entropy (unshocked) core, and a high entropy (shocked) outer half of baryon mass, the maximum angular momentum is signicantly lower. This leads to a minimum period of uniform rotationofcoldneutronstarsofbaryonmass 1: 5M ,formed directly(i.e.withoutasubsequentsignicantaccretionofmass) fromprotoneutronstarswithshockedenvelope,ofabout1.7 ms and strengthens the hypothesis that millisecond pulsars are ac- cretion accelerated neutron stars.

Solar mass

Stellar rotation

Source

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Citations (17)

Spin-up of the hyperon-softened accreting neutron stars

Astronomy and Astrophysics (2005)

J. L. Zdunik P. Haensel M. Bejger

We study the spin-up of the accreting neutron stars with a realistic hyperon-softened equation of state. Using precise 2D calculations we study the evolutionary tracks of accreting neutron stars in the angular-momentum – frequency planes. In contrast to the case of spinning-down solitary radio-pulsars, where a strong back-bending behavior has been observed, we do not see back-bending phenomena in the accretion-powered spinning-up case. We conclude that in the case of accretion-driven spin-up the back-bending is strongly suppressed by the mass-increase effect accompanying the angular-momentum increase.

Accretion disc

10.1051/0004-6361:20052832

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Citations (7)

Progenitor neutron stars of the lightest and heaviest millisecond pulsars

Astronomy and Astrophysics (2015)

M. Fortin M. Bejger P. Haensel J. L. Zdunik

The recent mass measurements of two binary millisecond pulsars, PSR J1614-2230 and PSR J0751+1807 with a mass M=1.97+/-0.04 Msun and M= 1.26 +/- 0.14 Msun, respectively, indicate a wide range of masses for such objects and possibly also a broad spectrum of masses of neutron stars born in core-collapse supernovae. Starting from the zero-age main sequence binary stage, we aim at inferring the birth masses of PSR J1614-2230 and PSR J0751+1807 by taking the differences in the evolutionary stages preceding their formation into account. Using simulations for the evolution of binary stars, we reconstruct the evolutionary tracks leading to the formation of PSR J1614-2230 and PSR J0751+1807. We analyze in detail the spin evolution due to the accretion of matter from a disk in the intermediate-mass/low-mass X-ray binary. We consider two equations of state of dense matter, one for purely nucleonic matter and the other one including a high-density softening due to the appearance of hyperons. Stationary and axisymmetric stellar configurations in general relativity are used, together with a recent magnetic torque model and observationally-motivated laws for the decay of magnetic field. The estimated birth mass of the neutron stars PSR J0751+1807 and PSR J1614-2230 could be as low as 1.0 Msun and as high as 1.9 Msun, respectively. These values depend weakly on the equation of state and the assumed model for the magnetic field and its accretion-induced decay. The masses of progenitor neutron stars of recycled pulsars span a broad interval from 1.0 Msun to 1.9 Msun. Including the effect of a slow Roche-lobe detachment phase, which could be relevant for PSR J0751+1807, would make the lower mass limit even lower. A realistic theory for core-collapse supernovae should account for this wide range of mass.

Millisecond

10.1051/0004-6361/201424911

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Citations (7)

Maximum mass of neutron stars and strange neutron-star cores

Astronomy and Astrophysics (2013)

J. L. Zdunik P. Haensel

Recent measurement of mass of PSR J1614-2230 rules out most of existing models of equation of state (EOS) of dense matter with high-density softening due to hyperonization, based on the recent hyperon-nucleon and hyperon-hyperon interactions, leading to a "hyperon puzzle". We study a specific solution of "hyperon puzzle", consisting in replacing a too soft hyperon core by a sufficiently stiff quark core. We construct an analytic approximation fitting very well modern EOSs of 2SC and CFL color superconducting phases of quark matter. This allows us for simulating continua of sequences of first-order phase transitions from hadronic matter to the 2SC, and then to the CFL state of color superconducting quark matter. We obtain constraints in the parameter space of the EOS of superconducting quark cores, resulting from M_max> 2 M_sol. We also derive constraints that would result from significantly higher measured masses. For 2.4 M_sol required stiffness of the CFL quark core should have been close to the causality limit, the density jump at the phase transition being very small. Condition M_max > 2 M_sol puts strong constraints on the EOSs of the 2SC and CFL phases of quark matter. Density jumps at the phase transitions have to be sufficiently small and sound speeds in quark matter - sufficiently large. A strict condition of thermodynamic stability of quark phase results in the maximum mass of hybrid stars similar to that of purely baryon stars. Therefore, to get M_max>2 M_sol for stable hybrid stars, both sufficiently strong additional hyperon repulsion at high density baryon matter and a sufficiently stiff EOS of quark matter would be needed. However, it is likely that the high density instability of quark matter (reconfinement) indicates actually the inadequacy of the point-particle model of baryons in dense matter at very high densities.

Dense matter

10.1051/0004-6361/201220697

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Citations (193)

Internal Heating in Magnetars: Role of Electron Captures

Journal of Physics Conference Series (2022)

N. Chamel A. F. Fantina Lami Suleiman J. L. Zdunik P. Haensel

Abstract The role of electron captures by nuclei in the shallow heating of magnetars is further investigated using both nuclear measurements and the theoretical atomic mass table HFB-27. Starting from the composition of the outer crust in full equilibrium, we have calculated the onset of electron captures and the heat released due to the slow decay of the magnetic field. Numerical results are found to be similar to those previously obtained with the HFB-24 atomic mass model and are consistent with neutron-star cooling data.

Magnetar

Internal heating

Atomic mass

Table (database)

10.1088/1742-6596/2340/1/012029

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Citations (0)

Fundamental physics and the absence of sub-millisecond pulsars

Astronomy and Astrophysics (2018)

B. Haskell J. L. Zdunik M. Fortin M. Bejger R. Wijnands

Context. Rapidly rotating neutron stars are an ideal laboratory to test models of matter at high densities. In particular, the maximum rotation frequency of a neutron star depends on the equation of state and can be used to test models of the interior. However, observations of the spin distribution of rapidly rotating neutron stars show evidence for a lack of stars spinning at frequencies higher than f ≈ 700 Hz, well below the predictions of theoretical equations of state. This has generally been taken as evidence of an additional spin-down torque operating in these systems, and it has been suggested that gravitational wave torques may be operating and be linked to a potentially observable signal. Aims. We aim to determine whether additional spin-down torques (possibly due to gravitational wave emission) are necessary, or if the observed limit of f ≈ 700 Hz could correspond to the Keplerian (mass-shedding) break-up frequency for the observed systems, and is simply a consequence of the currently unknown state of matter at high densities. Methods. Given our ignorance with regard to the true equation of state of matter above nuclear saturation densities, we make a minimal physical assumption and only demand causality, that is, that the speed of sound in the interior of the neutron star should be lower than or equal to the speed of light c . We then connected our causally limited equation of state to a realistic microphysical crustal equation of state for densities below nuclear saturation density. This produced a limiting model that gave the lowest possible maximum frequency, which we compared to observational constraints on neutron star masses and frequencies. We also compared our findings with the constraints on the tidal deformability obtained in the observations of the GW170817 event. Results. We rule out centrifugal breakup as the mechanism preventing pulsars from spinning faster than f ≈ 700 Hz, as the lowest breakup frequency allowed by our causal equation of state is f ≈ 1200 Hz. A low-frequency cutoff, around f ≈ 800 Hz could only be possible when we assume that these systems do not contain neutron stars with masses above M ≈ 2 M ⊙ . This would have to be due either to selection effects, or possibly to a phase transition in the interior of the neutron star that leads to softening at high densities and a collapse to either a black hole or a hybrid star above M ≈ 2 M ⊙ . Such a scenario would, however, require a somewhat unrealistically stiff equation of state for hadronic matter, in tension with recent constraints obtained from gravitational wave observations of a neutron star merger.

Saturation (graph theory)

10.1051/0004-6361/201833521

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Citations (13)

Innermost stable circular orbits around strange stars and kHz QPOs in low-mass X-ray binaries

arXiv (Cornell University) (2000)

J. L. Zdunik P. Haensel D. Rosińska Éric Gourgoulhon

Exact calculations of innermost stable circular orbit (ISCO) around rotating strange stars are performed within the framework of general relativity. Equations of state (EOS) of strange quark matter based on the MIT Bag Model with massive strange quarks and lowest order QCD interactions, are used. The presence of a solid crust of normal matter on rotating, mass accreting strange stars in LMXBs is taken into account. It is found that, contrary to neutron stars, above some minimum mass a gap always separates the ISCO and stellar surface, independently of the strange star rotation rate. For a given baryon mass of strange star, we calculate the ISCO frequency as function of stellar rotation frequency, from static to Keplerian configuration. For masses close to the maximum mass of static configurations the ISCO frequencies for static and Keplerian configurations are similar. However, for masses significantly lower than the maximum mass of static configurations, the minimum value of the ISCO frequency is reached in the Keplerian limit. Presence of a solid crust increases the ISCO frequency for the Keplerian configuration by about ten percent compared to that for a bare strange star of the same mass.

Strange quark

Exotic star

Low Mass

10.48550/arxiv.astro-ph/0002394

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Citations (5)