https://phys.org/news/2019-03-lisa-ultralight-bosons-supermassive-black.html

Ultralight bosons are theoretical particles such as axions—theory has also suggested that they might comprise dark matter. Other theories have suggested that if ultralight bosons do exist, they probably form in clouds around the event horizons of black holes. And if they do, they would probably have a Compton wavelength. Because such wavelengths are inversely proportional to their mass, the Compton wavelength for an ultralight boson would be quite large.

The researchers note that superradiance should happen if the Compton wavelength of an ultralight boson cloud turns out to be similar to a Schwarzschild radius (the distance from its center to its event horizon) of a given black hole. Superradiance refers to boson fields coupling with a black hole as it spins and pulling energy from it to the point that the boson cloud rotates at the same rate as the black hole. The researchers note that superradiance would change the gravitational wave signal generated from the black hole—something that LISA could detect because it would be able to filter out extraneous noise that typically limits the abilities of ground-based systems.

                                                            
                                    
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