Lower limit on the heat capacity of the neutron star core

Using the observation of four transiently-accreting neutron stars, the authors provide (under simple assumptions) a lower limit for the star core heat capacity. The limit rules out a large fraction of the core being made up of a quark color-flavor-locked phase. Future observations during cooling periods between accretion outbursts will further constrain the heat capacity and neutrino cooling luminosity of the core.