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Toomre Q Parameter

(Q, Q Parameter)
(stability criterion for differentially rotating disks)

The Toomre Q Parameter (Q Parameter) is a criterion for the stability of differentially rotating disks, devised by Alar Toomre, and constructed so that Q<1 implies instability.

Q = ———

The condition of Q > 1 is known as Toomre's Stability Criteria.

For a gaseous disk, it is often labeled Qgas, and for Molecular Clouds, the assumption is that >1 means no Star Formation, i.e., a stable disk, and <1 means star formation.

It has also been applied to stars in a disk Galaxy.

(fluid dynamics,mathematics)