Urca Cooling in Neutron Star Crusts and Oceans: Effects of Nuclear Excitations

TL;DR

This paper investigates how nuclear excitations influence Urca cooling in neutron star crusts and oceans, providing a new formula that accounts for excited states and showing significant effects on neutrino luminosity calculations.

Contribution

It introduces a novel expression for Urca neutrino luminosity that includes excited nuclear states, enhancing the accuracy of stellar cooling models.

Findings

Neutrino luminosities vary significantly with temperature when excited states are considered.

The new formula can produce results radically different from previous ground-state-only models.

Excited nuclear states have a substantial impact on Urca cooling efficiency.

Abstract

The excited-state structure of atomic nuclei can modify nuclear processes in stellar environments. In this work, we study the influence of nuclear excitations on Urca cooling (repeated back-and-forth beta decay and electron capture in a pair of nuclear isotopes) in the crust and ocean of neutron stars. We provide for the first time an expression for Urca process neutrino luminosity which accounts for excited states of both members of an Urca pair. We use our new formula with state-of-the-art nuclear structure inputs to compute neutrino luminosities of candidate Urca cooling pairs. Our nuclear inputs consist of the latest experimental data supplemented with calculations using the projected shell model. We show that, in contrast with previous results that only consider the ground states of both nuclei in the pair, our calculated neutrino luminosities for different Urca pairs vary sensitively with the environment temperature and can be radically different from those obtained in the one transition approximation.