They find a way to determine the mass of a supermassive black hole

A team of astronomers has discovered that the mass of a supermassive black hole can be determined by its relationship to the light it emits.
Supermassive black holes weigh between 100 and a million solar cells. Although they are usually located in the center of galaxies and emit practically no light, they can only be found by the effects of gravity, except in the case of accretion, the power of interstellar gas and the matter of nearby stars. In these cases, black holes emit light in the visible and ultraviolet range at set intervals ranging from a few hours to several decades.
According to the study published in the journal Science, American astrophysicists have found this finding after having compiled a database of 67 active supermassive black holes. The numbers show that the time of light emission from black holes is closely related to their mass.

The researchers concluded that the light emission is due to random fluctuations during the accretion process and they hope that the correlation they have found can also be used to detect light emission patterns from medium-mass black holes, a class of objects that has been difficult to detect so far.