The Great Wall: Urca Cooling Layers in the Accreted NS Crust

TL;DR

This paper reviews how urca cooling layers in the accreted neutron star crust influence observable thermal properties, highlighting the role of electron-capture/beta-decay cycles as a thermal barrier.

Contribution

It introduces the concept of urca layers acting as a thermal barrier in the neutron star crust and discusses their impact on observable phenomena.

Findings

Urca cycles can operate at high temperatures in the NS crust.

Urca layers create a thermal barrier, affecting heat flow.

Implications for neutron star observables are significant.

Abstract

Accreting neutron stars host a number of astronomical observables which can be used to infer the properties of the underlying dense matter. These observables are sensitive to the heating and cooling processes taking place in the accreted neutron star (NS) crust. Within the past few years it has become apparent that electron-capture/beta-decay (urca) cycles can operate within the NS crust at high temperatures. Layers of nuclei undergoing urca cycling can create a thermal barrier, or Great Wall, between heating occurring deep in the crust and the regions above the urca layers. This paper briefly reviews the urca process and the implications for observables from accreting neutron stars.