APOD: The Accretion Disk

This cool computer visualization shows spiral shock waves of an accretion disk. Accretion disks are disks of orbitting matter that are best seen in X-ray wavelengths. Accretion disks form in binary systems where a huge red giant with lots of mass siphons off its material to a smaller object with more gravitational pull. The smaller spinning object collects matter on its surface and emits radiation. This small object can be a white dwarf, which is what low and medium mass stars (Like our Sun) turn into at the end of their life; a neutron star, the super dense collapsed cores of really massive stars after they explode; or a black hole, which forms after a really really really massive star explodes and gravity collapses whatever matter is there. It is the densest state of matter in which no light can escape, but you can see the accretion disks where the black hole's sphere of influence has not penetrated.
Check out The Accretion Disk