Abstract

Particle physics models of dark matter, certain extensions to the Standard Model, and low energy limits of models of quantum gravity, predict the existence of an abundance of ultralight degrees of freedom in the universe. Gravitational wave observations can be used to probe this dark sector indirectly. Black hole superradiance, the process in which a black hole’s rotational energy is converted into a self-gravitating bosonic cloud, leads to the emission of strong approximately monochromatic gravitational radiation. We discuss the superradiance instability timescales, possible gravitational wave signatures and associated search strategies. Strong field dynamics of isolated or binary boson stars may be another way gravitational wave observations can probe the existence of new bosonic particles. These clumps of energy, forming via gravitational cooling from a large abundance of ultralight bosons, can become more compact than neutron stars, and hence, also pose as excellent candidates to test the black hole paradigm. We discuss boson star formation, stability and possible non-linear dynamics, focusing particularly on the more compact rotating stars.