Hydrostatic equilibrium of causally consistent and dynamically stable neutron star models

TL;DR

This paper demonstrates that the mass-radius relation for the stiffest EOS alone does not guarantee dynamical stability of neutron stars, and emphasizes the importance of the compatibility criterion for hydrostatic equilibrium.

Contribution

It introduces core-envelope models satisfying causality and shows the compatibility criterion is essential for stability analysis, refining previous stability conditions for neutron stars.

Findings

Mass-radius relation alone is insufficient for stability.

Compatibility criterion is necessary and sufficient for hydrostatic equilibrium.

Model explains glitch behaviors in pulsars.

Abstract

We show that the mass-radius $(M-R)$ relation corresponding to the stiffest equation of state (EOS) does not provide the necessary and sufficient condition of dynamical stability for the equilibrium configurations, since such configurations can not satisfy the `compatibility criterion'. In this connection, we construct sequences composed of core-envelope models such that, like the stiffest EOS, each member of these sequences satisfy the extreme case of causality condition, $v = c = 1$, at the centre. We, thereafter, show that the $M-R$ relation corresponding to the said core-envelope model sequences can provide the necessary and sufficient condition of dynamical stability only when the `compatibility criterion' for these sequences is `appropriately' satisfied. However, the fulfillment of `compatibility criterion' can remain satisfied even when the $M-R$ relation does not provide the necessary and sufficient condition of dynamical stability for the equilibrium configurations. In continuation to the results of previous study, these results explicitly show that the `compatibility criterion' {\em independently} provides, in general, the {\em necessary} and {\em sufficient} condition of hydrostatic equilibrium for any regular sequence. Beside its fundamental feature, this study can also explain simultaneously, both (the higher as well as lower) values of the glitch healing parameter observed for the Crab and the Vela-like pulsars respectively, on the basis of starquake model of glitch generation.