# Supermassive black hole

##### Article

May 28, 2022

A supermassive black hole is a black hole with a mass of 105-1011 solar masses. Supermassive black holes have been found at the center of many galaxies, including the Milky Way.

## Specific properties

Supermassive black holes have specific properties that distinguish them from smaller black holes: Paradoxically, the average density of a supermassive black hole (calculated by dividing the black hole's mass by its Schwarzschild volume) can be very small (even less than the density of air in the Earth's lower atmosphere). This is because the Schwarzschild radius is directly proportional to the mass, and the density is inversely proportional to the volume (that is, in this case, the density is inversely proportional to the Schwarzschild radius). Further, the volume of a spherical object (for example, the event horizon of a non-rotating black hole) is directly proportional to the cube of the radius. As a result, the average density of a black hole decreases as its mass increases: p 3 c 6 32 π M 2 G 3 . {\displaystyle \rho {\frac {3\,c^{6}}{32\pi M^{2}G^{3}}}.} Tidal forces near the event horizon are much weaker due to the fact that the central singularity is located so far from the horizon that a hypothetical astronaut traveling to the center of a black hole would not feel the effects of extreme tidal forces until they dive very deep into it. Supermassive black holes are the source of almost all cosmic neutrinos.

## Shaping

There is no generally accepted theory of the formation of black holes of such a mass. There are several hypotheses, the most obvious of which is the hypothesis that describes the gradual increase in the mass of a black hole by the accretion of matter onto a stellar-mass black hole. Another hypothesis suggests that supermassive black holes are formed when large gas clouds collapse and turn into a relativistic star with a mass of several hundred thousand solar masses or more. Such a star quickly becomes unstable to radial perturbations due to