It is generally accepted that the limit on the stable rotation of neutron stars is set by gravitationalradiation reaction (GRR) driven instabilities, which cause the stars to emit gravitational waves that carry angular momentum away from them. The instability modes are moderated by the shear viscosity and the bulk viscosity of neutron star matter. Among the GRR instabilities, the fmode instability plays a historically predominant role. In this work, we determine the instability periods of this mode for three different relativistic models for the nuclear equation of state (EoS) named DD2, ACB4, and GM1L. The ACB4 model for the EoS accounts for a strong firstorder phase transition that predicts a new branch of compact objects known as masstwin stars. DD2 and GM1L are relativistic mean field (RMF) models that describe the mesonbaryon coupling constants to be dependent on the local baryon number density. Our results show that the fmode instability associated with m=2 sets the limit of stable rotation for cold neutron stars (T≲1010 K) with masses between 1M⊙ and 2M⊙. This mode is excited at rotation periods between 1 and 1.4 ms (∼20% to ∼40% higher than the Kepler periods of these stars). For cold hypothetical masstwin compact stars with masses between 1.96M⊙ and 2.10M⊙, the m=2 instability sets in at rotational stellar periods between 0.8 and 1 millisecond (i.e., ∼25% to ∼30% above the Kepler period).
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Equation of state of hot dense hyperonic matter in the Quark–MesonCoupling (QMCA) model
ABSTRACT We report a new equation of state (EoS) of cold and hot hyperonic matter constructed in the framework of the quark–mesoncoupling (QMCA) model. The QMCA EoS yields results compatible with available nuclear physics constraints and astrophysical observations. It covers the range of temperatures from T = 0 to 100 MeV, entropies per particle S/A between 0 and 6, lepton fractions from YL = 0.0 to 0.6, and baryon number densities nB = 0.05–1.2 fm−3. Applications of the QMCA EoS are made to cold neutron stars (NSs) and to hot protoneutron stars (PNSs) in two scenarios: (i) leptonrich matter with trapped neutrinos (PNSI) and (ii) deleptonized chemically equilibrated matter (PNSII). We find that the QMCA model predicts hyperons in amounts growing with increasing temperature and density, thus suggesting not only their presence in PNS but also, most likely, in NS merger remnants. The nucleon–hyperon phase transition is studied through the adiabatic index and the speed of sound cs. We observe that the lowering of (cs/c)2 to and below the conformal limit of 1/3 is strongly correlated with the onset of hyperons. Rigid rotation of cold and hot stars, their moments of inertia and Kepler frequencies are also explored. The QMCA model results are compared with two relativistic models, the chiral mean field model (CMF), and the generalized relativistic density functional (GRDF) with DD2 (nucleononly) and DD2YT (full baryon octet) interactions. Similarities and differences are discussed.
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 Award ID(s):
 1748621
 NSFPAR ID:
 10221854
 Date Published:
 Journal Name:
 Monthly Notices of the Royal Astronomical Society
 Volume:
 502
 Issue:
 3
 ISSN:
 00358711
 Page Range / eLocation ID:
 3476 to 3490
 Format(s):
 Medium: X
 Sponsoring Org:
 National Science Foundation
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