Click on the images for larger views. Stellar and galactic black holes. They have masses of millions to more than a billion times that of the Sun and reside in the centers of many, if not all, galaxies. Astronomers are not certain how middleweight black holes form. A good guess is that they are the result of repeated collisions and mergers of stellar black holes and neutron stars.
Black holes represent the most extreme form of matter in the universe.
Gravity in their vicinity is superstrong and warps space-time so severely that nothing can escape from the holes' interiors, not even light. Furthermore, black holes try to gobble up everything that comes close to them. In the process, the matter is accelerated to near the speed of light and heated to millions of degrees. Most of the matter is swallowed by the black hole, never to be seen again. The rest is tossed out at relativistic speeds in two narrowly-focused jets in opposite directions from the plane of the accretion disk.