R-mode Stability of GW190814's Secondary Component as a Supermassive and Superfast Pulsar
Xia Zhou, Ang Li, Bao-An Li
Abstract:
The nature of GW190814's secondary component m2 of mass (2.50−2.67)M⊙ in the mass gap between the currently known maximum mass of neutron stars and the minimum mass of black holes is currently under hot debate. Among the many possibilities proposed in the literature, the m2 was suggested as a superfast pulsar while its r-mode stability against the run-away gravitational radiation through the Chandrasekhar-Friedman-Schutz mechanism is still unknown. Using those fulfilling all currently known astrophysical and nuclear physics constraints among a sample of 33 unified equation of states (EOSs) constructed previously by Fortin {\it et al.} (2016) using the same nuclear interactions from the crust to the core consistently, we compare the minimum frequency required for the m2 to rotationally sustain a mass higher than 2.50M⊙ with the critical frequency above which the r-mode instability occurs. We use two extreme damping models assuming the crust is either perfectly rigid or elastic. Using the stability of 19 observed low-mass x-ray binaries as an indication that the rigid crust damping of the r-mode dominates within the models studied, we find that the m2 is r-mode stable while rotating with a frequency higher than 870.2 Hz (0.744 times its Kepler frequency of 1169.6 Hz) as long as its temperate is lower than about 3.9×10^7K, further supporting the proposal that GW190814's secondary component is a supermassive and superfast pulsar.
https://arxiv.org/abs/2011.11934v2
What can be learned from a proto-neutron star's mass and radius?
Edwan Preau (APC, LUTH), Aurélien Pascal (LUTH), Jérôme Novak (LUTH), Micaela Oertel (LUTH)
Abstract:
We make extensive numerical studies of masses and radii of proto-neutron stars during the first second after their birth in core-collapse supernova events. We use a quasi-static approach for the computation of proto-neutron star structure, built on parameterized entropy and electron fraction profiles, that are then evolved with neutrino cooling processes. We vary the equation of state of nuclear matter, the proto-neutron star mass and the parameters of the initial profiles, to take into account our ignorance of the supernova progenitor properties. We show that if masses and radii of a proto-neutron star can be determined in the first second after the birth, e.g. from gravitational wave emission, no information could be obtained on the corresponding cold neutron star and therefore on the cold nuclear equation of state. Similarly, it seems unlikely that any property of the proto-neutron star equation of state (hot and not beta-equilibrated) could be determined either, mostly due to the lack of information on the entropy, or equivalently temperature, distribution in such objects.
https://arxiv.org/abs/2102.05923v1
Markov Chain Monte Carlo Predictions of Neutron-rich Lanthanide Properties as a Probe of r-process Dynamics
Nicole Vassh, Gail C. McLaughlin, Matthew R. Mumpower, Rebecca Surman
Abstract:
Lanthanide element signatures are key to understanding many astrophysical observables, from merger kilonova light curves to stellar and solar abundances. To learn about the lanthanide element synthesis that enriched our solar system, we apply the statistical method of Markov Chain Monte Carlo to examine the nuclear masses capable of forming the r-process rare-earth abundance peak. We describe the physical constraints we implement with this statistical approach and demonstrate the use of the parallel chains method to explore the multidimensional parameter space. We apply our procedure to three moderately neutron-rich astrophysical outflows with distinct types of r-process dynamics. We show that the mass solutions found are dependent on outflow conditions and are related to the r-process path. We describe in detail the mechanism behind peak formation in each case. We then compare our mass predictions for neutron-rich neodymium and samarium isotopes to the latest experimental data from the CPT at CARIBU. We find our mass predictions given outflows that undergo an extended (n,γ)⇄(γ,n) equilibrium to be those most compatible with both observational solar abundances and neutron-rich mass measurements.
https://arxiv.org/abs/2006.04322v2
Mass ejection in failed supernovae: equation of state and neutrino loss dependence
Mario Ivanov, Rodrigo Fernández
Abstract:
A failed core-collapse supernova from a non-rotating progenitor can eject mass due to a weakening of gravity associated to neutrino emission by the protoneutron star. This mechanism yields observable transients and sets an upper limit to the mass of the black hole (BH) remnant. Previous global simulations of this mechanism have included neutrino losses parametrically, however, with direct implications for the ejecta mass and energy. Here we evolve the inner supernova core with a spherically-symmetric, general-relativistic neutrino radiation-hydrodynamic code until BH formation. We then use the result in a Newtonian code that follows the response of the outer layers of the star to the change in gravity and resolves the surface pressure scale height. We find that the dense-matter equation of state (EOS) can introduce a factor ∼2 variation in gravitational mass lost to neutrinos, with a stiff EOS matching previous parametric results, and a soft EOS yielding lower ejecta masses and energies by a factor of several. This difference is caused primarily by the longer time to BH formation in stiffer EOSs. With a soft EOS, our red and yellow supergiant progenitors fail to unbind mass if hydrogen recombination energy is not included. Using a linear ramp in time for mass-energy lost to neutrinos (with suitable parameters) yields a stellar response within ∼10% of that obtained using the detailed history of neutrino losses. Our results imply quantitative but not qualitative modifications to previous predictions for shock breakout, plateau emission, and final BH masses from these events.
https://arxiv.org/abs/2101.02712v2
Urca Cooling in Neutron Star Crusts and Oceans: Effects of Nuclear Excitations
Long-Jun Wang, Liang Tan, Zhipan Li, G. Wendell Misch, Yang Sun
Abstract:
The excited-state structure of atomic nuclei can modify nuclear processes in stellar environments. In this work, we study the influence of nuclear excitations on Urca cooling (repeated back-and-forth beta decay and electron capture in a pair of nuclear isotopes) in the crust and ocean of neutron stars. We provide for the first time an expression for Urca process neutrino luminosity which accounts for excited states of both members of an Urca pair. We use our new formula with state-of-the-art nuclear structure inputs to compute neutrino luminosities of candidate Urca cooling pairs. Our nuclear inputs consist of the latest experimental data supplemented with calculations using the projected shell model. We show that, in contrast with previous results that only consider the ground states of both nuclei in the pair, our calculated neutrino luminosities for different Urca pairs vary sensitively with the environment temperature and can be radically different from those obtained in the one transition approximation.
https://arxiv.org/abs/2102.06010v1
DOI: 10.1016/j.physletb.2021.136138
Probing the boundary of phase transition of nuclear matter using proton flows in heavy-ion collisions at 2-8 GeV/nucleon
Ya-FeiGuo and Gao-ChanYong
Abstract:
Based on the relativistic transport model ART with the hadronic equation of state extended to have a phase transition via the use of the MIT bag model, properties of phase transition of dense nuclear matter formed in relativistic heavy-ion collisions are investigated. Proton sideward and directed flows are calculated with different equation of states in Au + Au collisions at beam energies of 2, 4, 6 and 8 GeV/nucleon. Compared with AGS experimental data in existence, the boundary of first-order phase transition is roughly confined, i.e., in the range of 2.5-4 times saturation density with temperature about 64-94 MeV. Such constraints are useful for ongoing RHIC Beam Energy Scan-II program to study the QCD matter phase diagram.
https://doi.org/10.1016/j.physletb.2021.136138
DOI: 10.1093/mnras/staa3489
Evolution of magnetic deformation in neutron star crust
Yasufumi Kojima, Shota Kisaka, Kotaro Fujisawa
Abstract:
We examine the magnetic field evolution occurring in a neutron star crust. Beyond the elastic limit, the lattice ions are assumed to act as a plastic flow. The Ohmic dissipation, Hall drift, and bulk fluid velocity driven by the Lorentz force are considered in our numerical simulation. A magnetically induced quadrupole deformation is observed in the crust during the evolution. Generally, the ellipticity decreases as the magnetic energy decreases. In a toroidal-field-dominated model, the sign of the ellipticity changes. Namely, the initial prolate shape tends to become oblate. This occurs because the toroidal component decays rapidly on a smaller time-scale than the poloidal dipole component. We find that the magnetic dipole component does not change significantly on the Hall time-scale of ∼1 Myr for the considered simple initial models. Thus, a more complex initial model is required to study the fast decay of surface dipoles on the above-mentioned time-scale.
https://doi.org/10.1093/mnras/staa3489
DOI: 10.1103/PhysRevLett.126.062501
Observation of Coulomb-Assisted Nuclear Bound State of Ξ – N System
Abstract:
In an emulsion-counter hybrid experiment performed at J-PARC, a Ξ− absorption event was observed which decayed into twin single-Λ hypernuclei. Kinematic calculations enabled a unique identification of the reaction process as Ξ−+14N→10ΛBe+5ΛHe. For the binding energy of the Ξ− hyperon in the Ξ−−14N system a value of 1.27±0.21 MeV was deduced. The energy level of Ξ− is likely a nuclear 1p state which indicates a weak ΞN–ΛΛ coupling.
https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.126.062501
DOI: 10.1103/PhysRevC.103.025801
Role of dense matter in tidal deformations of inspiralling neutron stars and in gravitational waveforms with unified equations of state
Abstract:
The role of dense-matter properties in the tidal deformability of a cold nonaccreted neutron star is further investigated. Using the set of Brussels-Montreal unified equations of state, we have computed the gravitoelectric Love numbers kl and the gravitomagnetic Love numbers jl up to l = 5. Their relative importance and their sensitivity to the symmetry energy and the neutron-matter stiffness are numerically assessed. Their impact on the phase of the gravitational-wave signal emitted by binary neutron star inspirals is also discussed.
https://journals.aps.org/prc/pdf/10.1103/PhysRevC.103.025801
DOI: 10.1016/j.nuclphysa.2021.122157
On the sound speed in hyperonic stars
T.F.Motta, P.A.M.Guichon and A.W.Thomas
Abstract:
We build upon the remarkable, model independent constraints on the equation of state of dense baryonic matter established recently by Annala et al. [1]. Using the quark-meson coupling model, an approach to nuclear structure based upon the self-consistent adjustment of hadron structure to the local meson fields, we show that, once hyperons are allowed to appear in dense matter in β-equilibrium, the equation of state is consistent with those constraints. As a result, while one cannot rule out the occurrence of quark matter in the cores of massive neutron stars, the available constraints are also compatible with the presence of hyperons.
https://doi.org/10.1016/j.nuclphysa.2021.122157
DOI: 10.1103/PhysRevC.103.025803
New equations of state constrained by nuclear physics, observations, and QCD calculations of high-density nuclear matter
S. Huth, C. Wellenhofer and A. Schwenk
Abstract:
We present new equations of state for applications in core-collapse supernova and neutron star merger simula- tions. We start by introducing an effective mass parametrization that is fit to recent microscopic calculations up to twice saturation density. This is important to capture the predicted thermal effects, which have been shown to determine the proto–neutron star contraction in supernova simulations. The parameter range of the energy-density functional underlying the equation of state is constrained by chiral effective field theory results at nuclear densities as well as by functional renormalization group computations at high densities based on QCD. We further implement observational constraints from measurements of heavy neutron stars, the gravitational wave signal of GW170817, and from the recent NICER results. Finally, we study the resulting allowed ranges for the equation of state and for properties of neutron stars, including the predicted ranges for the neutron star radius and maximum mass.
https://journals.aps.org/prc/pdf/10.1103/PhysRevC.103.025803