Constraints on Relic Magnetic Black Holes

Understand

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.