Accretion onto a small black hole at the center of a neutron star

TL;DR

This paper investigates the process and timescale of a small black hole embedded in a neutron star consuming it through accretion, using analytical models and full general relativity simulations to understand the system's evolution.

Contribution

It extends previous models by providing an analytical treatment of accretion rates and performing detailed numerical simulations of the entire evolution, including collapse.

Findings

Analytical accretion rates for neutron star matter onto small black holes.

Numerical simulations of black hole-neutron star systems across a wide mass range.

Expressions for the lifetime of neutron stars with embedded black holes.

Abstract

We revisit the system consisting of a neutron star that harbors a small, possibly primordial, black hole at its center, focusing on a nonspinning black hole embedded in a nonrotating neutron star. Extending earlier treatments, we provide an analytical treatment describing the rate of secular accretion of the neutron star matter onto the black hole, adopting the relativistic Bondi accretion formalism for stiff equations of state that we presented elsewhere. We use these accretion rates to sketch the evolution of the system analytically until the neutron star is completely consumed. We also perform numerical simulations in full general relativity for black holes with masses up to nine orders of magnitude smaller than the neutron star mass, including a simulation of the entire evolution through collapse for the largest black hole mass. We construct relativistic initial data for these simulations by generalizing the black hole puncture method to allow for the presence of matter, and evolve these data with a code that is optimally designed to resolve the vastly different length scales present in this problem. We compare our analytic and numerical results, and provide expressions for the lifetime of neutron stars harboring such endoparasitic black holes.