The effect of opacity on neutron star Type I X-ray burst quenching

TL;DR

This study investigates how increased opacity in the outer layers of neutron stars influences the accretion rate at which Type I X-ray bursts cease, addressing discrepancies between observed and predicted burst quenching thresholds.

Contribution

It demonstrates that higher opacity in the neutron star's outer layers can stabilize nuclear burning, potentially resolving the mismatch between theory and observations.

Findings

Higher opacity near the surface stabilizes nuclear burning.

Opacity variations significantly affect burst quenching thresholds.

Results suggest opacity plays a key role in burst stabilization.

Abstract

One long standing tension between theory and observations of Type I X-ray burst is the accretion rate at which the burst disappear due to stabilization of the nuclear burning that powers them. This is observed to happen at roughly one third of the theoretical expectations. Various solutions have been proposed, the most notable of which is the addition of a yet unknown source of heat in the upper layers of the crust, below the burning envelope. In this paper we ran several simulations using the 1D code MESA to explore the impact of opacity on the threshold mass accretion rate after which the bursts disappear, finding that a higher than expected opacity in the less dense layers near the surface has a stabilizing effect.