Black Hole

The concept of massive black holes at the centers of some galaxies is supported by theoretical investigations of the formation of very massive stars. Stars of more than about a hundred times (and less than about a million times) the mass of the Sun cannot form because they will explode from nuclear energy released during their contraction before the star can shrink enough for its self-gravity to hold it together. However, if a collapsing cloud of interstellar material contains more than about a million times the mass of the Sun, the collapse will occur so fast the nuclear processes initiated by the collapse will not be able to stop the collapse. The collapse will continue unrestrained until the object forms a black hole.

Such objects appear to be required to understand the observed behavior of the material in the center of some galaxies. Indeed, it is now certain that black holes reside at the centers of many normal galaxies, including our own Milky Way. Evidence comes from the motion of gas clouds near the galactic center and from the detection of x-rays bursts from the galactic center such as would typically be produced by a supermassive black hole swallowing matter.