Model of heat diffusion in the outer crust of bursting neutron stars

TL;DR

This paper models heat diffusion in the outer crust of neutron stars, revealing a heat-absorbing layer that influences star cooling and superburst phenomena, with implications for interpreting observational data.

Contribution

It introduces a new heat diffusion model for the neutron star crust, highlighting the heat-accumulating properties of a specific outer layer and its role in star cooling and superburst analysis.

Findings

The outer crust layer can absorb up to 10^{44} erg of heat.

A warm, decoupled layer acts as a heat reservoir for months.

Self-similar analysis helps estimate properties of bursting neutron stars.

Abstract

We study heat diffusion after an energy release in a deep spherical layer of the outer neutron star crust (10^7 < \rho < 4 x 10^{11} g/cm^3). We demonstrate that this layer possesses specific heat-accumulating properties, absorbing heat and directing it mostly inside the star. It can absorb up to about 10^{43}-10^{44} erg due to its high heat capacity, until its temperature exceeds T ~ 3 x 10^9 K and triggers a rapid neutrino cooling. A warm layer with T ~ 10^8 - 3 x 10^9 K can serve as a good heat reservoir, which is thermally decoupled from the inner crust and the stellar core for a few months. We present a toy model to explore the heat diffusion within the heat-accumulating layer, and we test this model using numerical simulations. We formulate some generic features of the heat propagation which can be useful, for instance, for the interpretation of superbursts in accreting neutron stars. We present a self-similar analysis of late afterglow after such superbursts, which can be helpful to estimate properties of bursting stars.