Cooling of neutron stars and hybrid stars with a stiff hadronic EoS

TL;DR

This paper explores how stiff hadronic equations of state and phase transitions to quark matter influence neutron star cooling, successfully explaining observed temperature-age data across a broad mass range.

Contribution

It demonstrates that incorporating a stiff nuclear EoS and a phase transition to quark matter can account for diverse neutron star cooling observations.

Findings

Stiff EoS allows neutron star masses up to ~2.4 M_sun.

Hybrid stars with quark cores can explain rapid cooling of CasA.

Cooling curves are consistent with observed data across a wide mass spectrum.

Abstract

Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of neutron stars with masses in a broad range from $\sim 1.2$ to 2 $M_\odot$. The values $M>2 M_{\odot}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4 M_\odot$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of $2.426 M_\odot$ for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass $1.674 M_\odot$.