Constraining extremely light axion-like particles is usually very difficult since their interaction strength with photons and matter typically decreases as their mass decreases. However, one fascinating way to exclude, or provide evidence for, the existence of such particles is via the process of black hole superradiance. The mere existence of a boson field around a black hole is sufficient to start extracting energy and spin from the black hole and grow a cloud of bosons around it. This effect is in contradiction to observing fast-spinning black holes, which can be used to derive constraints on the boson mass.

In our new preprint [arXiv:2406.10337], we explore how to improve the statistical analysis of obtaining such constraints: first, by doing a more rigorous analysis and, second, by proposing a method that can extract more information from future black hole data analyses.

In the spirit of the AxiTools project, the accompanying code for our analysis is publicly available on Github.