Astrophysical disk
= Astrophysical disk
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= Astrophysical disc
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An \b[astrophysical disk] is a flattened, rotating distribution of matter. Examples include a young <star>'s <protoplanetary disk>, an <accretion disk> around a compact object and a stellar <galactic disk>. For gas that can radiate away random-motion <energy> while retaining <angular momentum>, settling into a disk is easier than falling directly toward the center. Ordered orbital motion supplies radial support; <pressure>, random motions or magnetic forces determine the thickness. The same geometry therefore contains systems with very different heating and transport mechanisms.