Accretion Disk
Cygnus X-1
Image from Steve Bowers
The accretion disk around Cygnus X-1, a black hole near the edge of Terragen space
Whirling disk of hot gas and dust around a large compact object such as a white dwarf, neutron star, or black hole, usually material that has been thrown off one star and is being drawn into the companion object.

Accretion disks also form around most stars in the early stages of their development, as the pre-stellar cloud collapses under gravity. The disk around such protostars will eventually coalesce into planets, although some dust and debris invariably is left over.
t tauri star
Image from Steve Bowers
A T Tauri star, a protostar with similar mass to Sol
 
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Development Notes
Text by M. Alan Kazlev and Steve Bowers

Initially published on 31 December 2001.