Speaker
Description
Black hole (BH) superradiance is a powerful probe of ultralight axions. If nature contains a boson with a mass of order $10^{-12}$ eV, vacuum fluctuations will lead to its efficient production around spinning stellar mass BHs, forming a gravitational atom that both drains the BH spin and decays to produce near-monochromatic gravitational waves. Existing superradiance constraints derive primarily from spin measurements of a handful of identified BHs, but in this talk I will present a detailed study of the understudied population level effect: gravitational waves arising from both the 100 million BHs in the Milky Way and the stochastic signal from axion clouds throughout the universe. We study the impact of a broad range of systematic uncertainties on the BH properties and compute the projected axion sensitivity for LIGO, as well as future instruments including high-frequency detectors, which, in the most optimistic cases, could reach the lowest masses available to the projected sensitivity of axion dark matter searches. I will then discuss related current work explicitly illustrating how LVK observations of BH populations can lead to multiple pathways for further probing axions.