From TheBestLinks.com
An accretion disk (or accretion disc) is a structure formed by material falling into a gravitational source. Conservation of angular momentum requires that, as a large cloud of material collapses inward, any small rotation it may have will increase. Centrifugal force causes the rotating cloud to collapse into a disk, and tidal effects will tend to align this disk's rotation with the rotation of the gravitational source in the center. Friction between the particles of the disk generates heat and saps orbital momentum, causing material in the disk to spiral inward until it impacts on the central body.
The most spectacular accretion disks found in nature are those of active galactic nuclei. As matter spirals into a black hole, the intense gravitational gradient gives rise to intense frictional heating; the accretion disk of a black hole is hot enough to emit x-rays just outside of the event horizon.
Artist's conception of binary systems with one black hole
Often, in binary systems with one black hole, observations show matter being pulled from the visible star into the black hole's accretion disk. The largest and most voracious black holes known are those which form the cores of quasars, whose accretion disks emit more radiation than entire galaxies of stars.
Protoplanetary discs are referred to as accretion disks when viewed as material falling into the central protostar.
See also:
Literature:
- Accretion power in astrophysics, Frank, King, Raine, Cambridge University Press, 1985
de:Akkretionsscheibe
fr:Disque d'accrétion
it:Disco di accrescimento
pl:Dysk akrecyjny
Related links
Top visited
0 of
0 links
[no links posted yet]
>> place link >>
Discussion
Last posted
0 of
0 messages
[no messages posted yet]
>> post message >>
Watch
You can
add this article to your own "watchlist" and receive e-mail notification about all changes in this page.
