Black holes have a preference for forming around two "universal" masses equivalent to about nine and 16 times the mass of our sun, according to a new study of the frequency of the gravitational-wave ‘chirps’ released when two black holes collide and merge. These findings could ultimately pave the way for an independent measure of the expansion of the Universe.
Since 2015, 90 gravitational-wave events have been identified by detectors at sites specifically built to find these information-rich ripples in spacetime. This includes laboratories such as the Laser Interferometer Gravitational-wave Observatory (LIGO) in the US, its sister site, Virgo, in Italy and the Kamioka Gravitational-Wave Detector (KAGRA) in Japan. Each merger produces what's known as a chirp, which is a blast of gravitational waves that rapidly increase in frequency as two black holes spiral closer and closer around one another before colliding and merging. The frequency and amplitude of this chirp is connected to the mass of the black holes that have merged; their combined mass is sometimes referred to as the "chirp mass."
