Black Holes

A black hole is a region of spacetime from which nothing, not even light, can escape. The boundary or "surface" of a black hole is called an event horizon.

Physicists think black holes form from a number of physical processes, including stellar collapse, collapse of galactic cores, and collapse of matter in the early universe. Black holes develop in all of these cases when a large enough quantity of matter and energy accumulates in a small enough region of spacetime. Then, no known law of physics can stop the collapse, and all the mass of the object collapses down to a singularity, where the force of gravity is infinite.

Let's examine briefly all of these cases in turn, starting with stellar collapse. When the nuclear furnace that powers a star goes out, the star starts to collapse because the pressure caused by the heat from the nuclear furnace in its core no longer counteracts the force of gravity. The star contracts until it either forms a white dwarf, a neutron star, or a black hole. The end result depends on the initial mass of the star, and on the amount of matter that the star ejects before and during the collapse. Black holes formed by stellar collapse typically have masses of a few solar masses.

The central core of a galaxy accumulates matter, in the form of stars and gas, by a variety of ways. When stars get close to each other, gravity changes the orbits of the stars, causing some stars to plunge into the central core. Gas accumulates in the central core as the result of friction. Eventually, the cental core aquires so much matter that a gigantic black hole forms. The black holes that inhabit central cores of galaxies range in mass from millions to billions of solar masses!

The primordial matter in the universe just after the big bang did not have completely uniform density. Regions of high density might have collapsed to form primordial black holes having a very wide range of masses.

Home