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Ed Brown Colloquium Abstract (Jan 31, 2018)

The Densest Matter in the Observable Universe: Accreting Neutron Stars and the Physics of Dense Matter

Neutron stars are composed of the densest observable matter in nature and occupy the intellectual frontier between astrophysics, nuclear physics, and, now, gravitational physics. Current and planned nuclear experiments on heavy nuclei and observations of neutron stars in both electromagnetic and gravitational waves  will be exploring the nature of dense matter from complimentary approaches. Many observed neutron stars accrete hydrogen- and helium-rich matter from a companion star. During the slow compression to nuclear density the accreted matter is transmuted from being proton-rich to being proton-poor. These reactions affect many observable phenomena - from energetic explosions on the neutron star's surface to cooling of the surface layers - that in turn inform us about the nature of the deep interior of the neutron star. In this talk, I shall describe what recent astronomical observations and nuclear physics experiments are telling us about the nature of matter at nuclear densities.

Technical Talk: Inferences on the Specific Heat and Neutrino Emissivity of Dense Matter from Two Accreting Neutron Stars

Many neutron stars are in binaries and accrete matter transferred from their companion. Often, this accretion is intermittent: the neutron star accretes rapidly for a time, and then is quiescent. In this talk, I will discuss recent efforts (Cumming et al. 2017, PRC 95: 025806, arXiv:1608.07532 and Brown et al. 2018, PRL, submitted, arXiv:1801.00041) to constrain the core heat capacity and neutrino emissivity of matter at densities above nuclear saturation from observations of the surface temperatures of quiescent neutron star transients immediately following an accretion outburst. In particular, I will show that a non-trivial lower bound can be placed on the heat capacity of the neutron star in KS1731-260, and that it cannot have rapid neutrino emission from its core. In contrast, the neutron star in MXB 1659-29 must have rapid neutrino cooling in its core. Further monitoring observations can potentially measure the specific heat of MXB 1659-29 and give us a better understanding of the dense matter equation of state.