Topic: "A Maximum Spin from Black Hole Mergers" (Video)
ABSTRACT: The famous "no hair" theorem implies that astrophysical black holes are fully described by their mass M and spin angular momentum S. However, if S grows above GM^2/c the black hole becomes a naked singularity unclothed by an event horizon. The cosmic censorship conjecture postulates that such naked singularities cannot occur in nature, but has never been proven to hold for the black holes produced in finite mass-ratio black-hole mergers. Understanding black-hole spins is also important for astrophysics. Supermassive black holes grow through two channels: continuous gas accretion and discrete binary mergers. The distribution of black-hole spins may help us determine the relative importance of these two channels in different environments. I will discuss the spins black holes acquire through both gas accretion and binary mergers, and present a new limit to black-hole spins in test-particle mergers.