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In astrophysics, accretion is the growth of particles into a massive object by gravitationally attracting more matter, typically gaseous matter in an accretion disc. This attracted matter accelerates the growth of the particles into boulder-sized planetesimals. The more massive planetesimals accrete some smaller ones, while others shatter in collisions. Accretion discs 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 disc 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 formation of terrestrial planets differs from that of Jovian planets. The particles that made up the terrestrial planets were made from metal and rock that condensed in the inner Solar System. However, the Jovian planets began as large, ice planetesimals, which then captured hydrogen and helium gas from the solar nebula. The planetesimals which form the two types of planets differ due to the frost line (astrophysics).
The Jovian protoplanets probably[according to whom?] 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.
- "Science with the VLTI". European Southern Observatory. 2008-08-08. Archived from the original on 24 May 2011. Retrieved 2011-04-11.
- Donahue, Megan, Nicholas Schneider, and Mark Voit. "Formation of the Solar System." The Essential Cosmic Perspective. By Jeffrey Bennett. Seventh ed. San Francisco: Pearson Education, 2014. 136-69. Print.
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