How is the mass of a black hole measured?

The mass of a black hole is measured through observations of its gravitational effects on surrounding matter.

Black holes are objects with such strong gravitational fields that nothing, not even light, can escape from them. Therefore, they cannot be directly observed. Instead, scientists measure the effects of a black hole's gravity on surrounding matter, such as stars or gas clouds.

One method of measuring a black hole's mass is through observations of stars orbiting around it. By analyzing the orbits of these stars, scientists can calculate the mass of the black hole that they are orbiting.

Another method is through observations of the accretion disk, a disk of gas and dust that surrounds the black hole. As matter falls into the black hole, it heats up and emits radiation, which can be detected by telescopes. By analyzing the properties of this radiation, scientists can estimate the mass of the black hole.

Finally, gravitational waves can also be used to measure the mass of a black hole. When two black holes merge, they create ripples in spacetime known as gravitational waves. By analyzing the properties of these waves, scientists can determine the masses of the black holes that merged.

Overall, the mass of a black hole is measured indirectly through observations of its gravitational effects on surrounding matter, using a variety of methods including star orbits, accretion disks, and gravitational waves.