Accretion (astrophysics)

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Artist's impression of a binary system with an accretion disk surrounding a black hole

In astrophysics, the term accretion is used for at least two distinct processes.

The first and most common is the growth of a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disk.[1] Accretion disks are common around smaller stars or stellar remnants in a close binary or black holes in the centers of spiral galaxies. Some dynamics in the disk are necessary to allow orbiting gas to lose angular momentum and fall onto the central massive object. Occasionally, this can result in stellar surface fusion. (See: Bondi accretion)

The second process is somewhat analogous to the one in atmospheric science. In the nebular theory, accretion refers to the collision and sticking of cooled microscopic dust and ice particles electrostatically, in protoplanetary disks and gas giant protoplanet systems, eventually leading to planetesimals which gravitationally accrete more small particles and other planetesimals.[citation needed]

Use of the term accretion disk for the protoplanetary disk thus leads to confusion over the planetary accretion process, although in many cases it may well be that both accretion processes are happening simultaneously. T Tauri is an example of this phenomenon.


The Jovian protoplanets probably had disks of their own, in close analogy to the Solar System as a whole. A Jovian protoplanet may accrete gas from its surrounding protoplanetary disk, as in the first process; at the same time, dust and ice particles in the disk would accrete into moonlets and ring systems, as in the second process.

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  1. ^ "Science with the VLTI". European Southern Observatory. 2008-08-08. Archived from the original on 24 May 2011. Retrieved 2011-04-11.