Detectability of gravitational waves from superradiant instabilities of scalar fields

Incident waves scattering off a black hole may get amplified at the expense of the rotational energy of the hole. Because of this process, known as superradiance, ultralight massive bosonic fields can form a non-axisymmetric cloud around the black hole due to repeated amplification. The growth of this bosonic cloud leads to emission of gravitational radiation, that could in principle be detected by ground-based gravitational wave detectors if the boson has mass $\sim 10^{-12}$eV or by LISA for masses $\sim 10^{-17}$eV. Therefore astrophysical black holes can serve as particle detectors. In the absence of detections, we can rule out the existence of bosons in the corresponding mass range. We explore near-term and long-term prospects for observing such events through follow-up searches of the continuous waves that would be emitted after black hole merger events of the kind detected by the LIGO/Virgo collaboration.