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| ==Etymology== | | ==Etymology== |
| [[Latin]] accretion-, accretio, from accrescere | | [[Latin]] accretion-, accretio, from accrescere |
− | *Date: [http://www.wikipedia/org/wiki/17th_Century 1615] | + | *Date: [https://www.wikipedia/org/wiki/17th_Century 1615] |
| ==Definitions== | | ==Definitions== |
| *1 : the process of growth or enlargement by a gradual buildup: as a : increase by external addition or accumulation (as by adhesion of external parts or particles) b : the increase of land by the action of natural forces | | *1 : the process of growth or enlargement by a gradual buildup: as a : increase by external addition or accumulation (as by adhesion of external parts or particles) b : the increase of land by the action of natural forces |
| *2 : a product of accretion; especially : an extraneous addition <accretions of grime> | | *2 : a product of accretion; especially : an extraneous addition <accretions of grime> |
| ==Description (Physics)== | | ==Description (Physics)== |
− | An '''accretion disc''' is a [[structure]] (often a circumstellar disk) formed by [[diffuse]] [[material]] in orbital [[motion]] around a central [[body]]. The central body is typically a young [[star]], a [http://en.wikipedia.org/wiki/Protostar protostar], a [http://en.wikipedia.org/wiki/White_dwarf white dwarf], a [http://en.wikipedia.org/wiki/Neutron_star neutron star], or a [http://en.wikipedia.org/wiki/Black_hole black hole]. [[Gravity]] causes material in the disc to spiral inward towards the central body. Gravitational [[forces]] compress the material causing the emission of [http://www.wikipedia.org/wiki/Electromagnetic_Radiation electromagnetic radiation]. The [[frequency]] range of that radiation depends on the central object. Accretion discs of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the x-ray part of the [[spectrum]].[http://en.wikipedia.org/wiki/Accretion_disk] | + | An '''accretion disc''' is a [[structure]] (often a circumstellar disk) formed by [[diffuse]] [[material]] in orbital [[motion]] around a central [[body]]. The central body is typically a young [[star]], a [https://en.wikipedia.org/wiki/Protostar protostar], a [https://en.wikipedia.org/wiki/White_dwarf white dwarf], a [https://en.wikipedia.org/wiki/Neutron_star neutron star], or a [https://en.wikipedia.org/wiki/Black_hole black hole]. [[Gravity]] causes material in the disc to spiral inward towards the central body. Gravitational [[forces]] compress the material causing the emission of [https://www.wikipedia.org/wiki/Electromagnetic_Radiation electromagnetic radiation]. The [[frequency]] range of that radiation depends on the central object. Accretion discs of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the x-ray part of the [[spectrum]].[https://en.wikipedia.org/wiki/Accretion_disk] |
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| [[Category: Physics]] | | [[Category: Physics]] |
| [[Category: General Reference]] | | [[Category: General Reference]] |