http://arxiv.org/abs/1910.05767
The observation of rapidly-rotating neutron stars (in comparison with non-rotating ones) may provide even richer information on the behavior of the properties of nuclear matter at high densities. In the present work we provide a theoretical treatment concerning the effects of the upper bound of the speed of sound in dense matter on the bulk properties of rapidly-rotating (at Kepler limit) neutron stars. In particular, we consider two upper bounds for the speed of sound, $\upsilon_{s} = c$ and $\upsilon_{s} = c/\sqrt{3}$, and the one provided by the kinetic theory. We investigate to what extent the possible predicted (from various theories and conjectures) upper bounds on the speed of sound constraints the ones of various key quantities, including the maximum mass and the corresponding radius, Keplerian frequency, Kerr parameter and moment of inertia. We mainly focus on the lower proposed limit, $\upsilon_{s}=c/\sqrt{3}$, and we explore in which mass region a rotating neutron star collapses to a black hole. In any case, useful relations of the mentioned bulk properties with the transition density, are derived and compared with the case of non-rotating neutron stars. We concluded that the limit $\upsilon_{s}=c/\sqrt{3}$, leads to dramatic decrease on the values of the maximum mass, Kerr parameter and moment of inertia preventing a neutron star to reach values which derive from other consideration or constraints.
C. Margaritis, P. Koliogiannis and C. Moustakidis
Tue, 15 Oct 19
34/90
Comments: 8 pages, 10 figures, 2 tables