It is now believed that at the center of each galaxy there is a super-massive black hole that is millions to billions of times heavier than our sun. The massive black hole captures nearby stars and drags them into a swirling accretion disk. A torus in the inner accretion shields the black hole in those systems that are viewed edge on (which is probably the case for our galactic center). In many of these systems, a jet is ejected perpendicular to the disk and is seen in the optical and radio wavebands. In the very central regions the disk becomes so hot (tens of millions of degrees) that the emission is in the X-ray and Gamma-ray bands. Black Holes remain one of the most mysterious objects in the Universe. Not only are Black Holes invisible to detection but physicists think that they are one of the few places in the Universe that the most fundamental laws of physics break-down.

This animation shows an artist's impression of the view from an approaching spaceship. The HEASARC data archives contain many observations of these systems made with orbiting X-ray and Gamma-ray observatories.