Tidal effects on primordial black hole capture in neutron stars

TL;DR

This paper investigates how tidal forces from nearby celestial bodies can influence the capture of primordial black holes by neutron stars, potentially weakening existing constraints on dark matter composed of such black holes.

Contribution

It introduces the impact of tidal perturbations on PBH capture by neutron stars and provides analytical formulas for capture rates, highlighting environmental dependencies.

Findings

Tidal effects can prevent PBHs from being captured in certain environments.

Tidal perturbations weaken constraints on PBH dark matter for masses below 10^{22} g.

Analytical formulas for capture rates are derived.

Abstract

We revisit the problem of the capture of a primordial black hole (PBH) by a neutron star, accounting for the tidal perturbation from a nearby star or planet. For asteroid-mass PBHs, which could constitute all of the dark matter in the universe, a weakly bound post-capture orbit could be tidally disturbed to the point of preventing the PBH from settling in the neutron star and consuming it within a cosmologically short timescale. We show how this effect depends on environmental parameters and can weaken the proposed constraints based on observations of old neutron stars in high-density dark matter environments for PBH masses $\lesssim 10^{22}\,$g. We also provide approximate analytical formulae for the capture rates.