Equation of state of dense matter and maximum mass of neutron stars

Abstract

Abstract. Theoretical models of the equation of state (EOS) of neutronstar matter (starting with the crust and ending at the densest region of the stellar core) are reviewed. Apart from a broad set of baryonic EOSs, strange quark matter, and even more exotic (abnormal and Q-matter) EOSs are considered. Results of calculations of Mmax for non-rotating neutron stars and exotic compact stars are reviewed, with particular emphasis on the dependence on the dense-matter EOS. Rapid rotation increases Mmax, and this effect is studied for both neutron stars and exotic stars. Theoretical results are then confronted with measurements of masses of neutron stars in binaries, and the consequences of such a confrontation and their possible impact on the theory of dense matter are discussed.

Hyperon softening of the EOS of dense matter and the spin evolution of isolated neutron stars

“…The softening of the EOS by hyperonization of matter can be also visualized by comparing the values of the maximum allowable mass for non-rotating neutron stars, M max , for the EOS without hyperons, referred hereafter as the N EOS, and those involving nucleons and hyperons (NH). Typically, allowing for the presence of hyperons lowers the value of M max by (0.3−0.6) M (see, e.g., Haensel 2003). The presence of hyperons leads to a very characteristic flattening of the massradius and mass-central density plot for neutron star, with a knee taking place just after the threshold for the first hyperon (Glendenning 1985;Balberg et al 1999).…”

The Role of Magnetic Fields in Gamma-Ray Bursts from SNeII

“…Calculations show that a NS generally has a surface density of [13,14] and a central density ranging between and depending on the mass of the NS. These figures clearly indicate that, under normal circumstances, there is a huge radial plasma density gradient within any NS.…”

Physics of Accretion Flows around Compact Objects

“…there exist a whole bunch of EOS that could describe matter at these supernuclear densities. If ρu ∼ < 2ρ0 the contribution of the outer layers (ρ < ρu) of the neutron star to the maximum mass is negligible (for this and the following see the excellent lectures by Haensel [34]). The maximum mass of neutron stars with causal (cs ≤ c, where cs is the adiabatic speed of sound) EOSs is only slightly increased by rotation: M rot max ≃ 1.18M stat max [35].…”

“…All members of the lower mass set are confirmed neutron stars, i.e. they are either (radio or X-ray) pulsars or X-ray bursters 1 The member of the higher mass set are certainly not neutron stars since the maximum mass of these celestial bodies satisfies the inequality [34] Mmax ≤ M CL max = 3.0 5 × 10 14 g cm −3 ρu…”

“…They generated some astrophysical interest because the maximum mass of Q-stars could be as large as ∼ 10M⊙. However, in fact these high mass value were obtained by allowing sufficiently low values of the fiducial density ρu [34]. Of course we don't know what it could be in reality.…”