Extremal Kerr Black Hole Dark Matter from Hawking Evaporation

The Hawking process results in a monotonic decrease of the black hole mass,but a biased random walk of the black hole angular momentum. We demonstratethat this stochastic process leads to a significant fraction of primordialblack holes becoming extremal Kerr black holes (EKBHs) of one to a few Planckmasses regardless of their initial mass. For these EKBHs, the probability ofever absorbing a photon or other particle from the cosmic environment is small,even in the cores of galaxies. Assuming that EKBHs are stable, they behave ascold dark matter, and can comprise all of the dark matter if they are formedwith the correct initial abundance.