Keplerian disk

A Keplerian disk is a disk of material that follows Kepler's laws of motion in conjunction with a central body. The laws specify an angular rotation rate rate of the disk at each distance from the center, rates which are higher toward the center of the disk and lower further away. The Keplerian disk concept is somewhat ideal, serving as a first approximation, because it is based only upon the force of gravity between disk material and the central body. The concept can reasonably model a circumstellar disk, or ring around a planet, both of which generally follow Kepler's laws for the most part, but other forces make portions of the disk diverge from normal Keplerian orbit. Such other forces are the gas pressure of the disk material and radiation pressure from the central star, which can add to the "push" away from the star, thus once the dynamics have found a stable state, the material is rotating slower than it would in a pure Keplerian orbit. The effects of gravitation between portions of the disk (the disk's self-gravitation) are also discounted. Actual disks presumed to be very close to the Keplerian-disk model may be referred to as Keplerian disks.