They estimate masses through their gravitational effect on other objects, such as the gas and dust in an accretion disk orbiting around a black hole. Today in class we have been discussing black holes that result from the collapse of a stars. There is another kind of black hole that can form at the center of a galaxy, a supermassive black hole. Now go back and revise questions 1 and 2. This is space-time squeezed in on itself.
Schwartzschild radius depends on mass of black hole for the size of the event horizon .
For the person going into a black hole, the feet would be stretched first because of tidal forces. Friction would cause heat and x-ray production. Black holes are black because gravity is so strong. Gravity is strong because mass is high for very small object. It appears as a band fuzzy light across the sky.