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In astrophysics, particularly the study of accretion disks, the epicyclic frequency is the frequency at which a radially displaced fluid parcel will oscillate. It can be referred to as a "Rayleigh discriminant". When considering an astrophysical disc with differential rotation , the epicyclic frequency is given by : , where R is the radial co-ordinate.〔p161, Astrophysical Flows, Pringle and King 2007〕 This quantity can be used to examine the 'boundaries' of an accretion disc - when becomes negative then small perturbations to the (assumed circular) orbit of a fluid parcel will become unstable, and the disc will develop an 'edge' at that point. For example, around a Schwarzschild black hole, the Innermost Stable Circular Orbit (ISCO) occurs at 3x the event horizon - at . For a Keplerian disk, . == References == 〔 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Epicyclic frequency」の詳細全文を読む スポンサード リンク
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