The cooling of the Cassiopeia A neutron star as a probe of a triplet neutron pairing in the core

TL;DR

This paper investigates the rapid cooling of the Cassiopeia A neutron star to probe neutron superfluidity in its core, finding that conventional triplet superfluid models cannot explain the observed cooling behavior.

Contribution

It provides a detailed analysis of neutron star cooling, showing that standard $^3$P$_2$ superfluid models are insufficient to explain Cas A's rapid cooling, suggesting alternative superfluid states.

Findings

Conventional $^3$P$_2$ superfluid models do not account for Cas A's rapid cooling.

The cooling sensitivity depends on neutron star mass and envelope composition.

Alternative superfluid phase states may be needed to explain observations.

Abstract

The observed rapid cooling of the Cassiopeia A neutron star (Cas A NS) can be interpreted as being triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). This provides a unique possibility for probing the neutron condensate in the core. Using consistent neutron star core and crust equation of state and composition, I explore the sensitivity of this interpretation to the phase state of the triplet superfluid condensate. Modeling cooling within an expected range of neutron star masses and envelope compositions, I found that the fast cooling of the Cas A NS can not be explained by the PBF processes in the conventional $^3$P$_2$ condensate with $m_{j}=0$.