Constraints on Relic Magnetic Black Holes

TL;DR

This paper reviews current constraints on the abundance of extremally magnetically charged black holes, highlighting astrophysical limits and their potential role in cosmic phenomena.

Contribution

It provides a comprehensive analysis of observational bounds on magnetic black holes, including new limits from white dwarf destruction and proton decay catalysis.

Findings

White dwarf destruction constrains intermediate-mass black holes.

Intergalactic gas heating limits heavier magnetic black holes.

Magnetic black holes could catalyze proton decay, affecting astrophysical processes.

Abstract

We present current direct and astrophysical limits on the cosmological abundance of black holes with extremal magnetic charge. Because they don't Hawking radiate, much lighter primordial black holes could exist today if they are extremal. The dominant constraints come from white dwarf destruction for intermediate masses, and intergalactic gas heating for heavier black holes. Extremal magnetic black holes may catalyze proton decay, and thus we derive robust limits -- independent of the catalysis cross section -- from the above as well as from white dwarf heating. We discuss other bounds such as those from neutron star heating, solar neutrino production, binary formation and annihilation into gamma rays, and magnetic field destruction. We note that stable magnetically charged black holes can assist in the formation of neutron star mass black holes.