Editing Instability (section)

==Instabilities of stellar systems==

[[Galaxies]] and [[star cluster]]s can be unstable, if small perturbations in the [[gravitational potential]] cause changes in the density that reinforce the original perturbation.  Such instabilities usually require that the motions of stars be highly correlated, so that the perturbation is not "smeared out" by random motions. After the instability has run its course, the system is typically "hotter" (the motions are more random) or rounder than before. Instabilities in stellar systems include:

* [[Bar instability]] of rapidly rotating disks
* [[Jeans instability]]
* [[Firehose instability]]<ref name="MS94">{{citation
 | last1 = Merritt | first1 = D.
 | author1-link = David Merritt
 | last2 = Sellwood | first2 = J.
 | title=Bending Instabilities of Stellar Systems
 | journal=The Astrophysical Journal
 | volume=425
 | year=1994
 | pages=551–567
 | doi=10.1086/174005
 | bibcode=1994ApJ...425..551M
}}</ref>
* [[Gravothermal instability]]<ref>{{citation
 | title=The Gravothermal Instability at All Scales: From Turnaround Radius to Supernovae
 | last=Roupas | first=Zacharias
 | journal=Universe | volume=5 | issue=1 | page=12
 | date=January 2019 | doi=10.3390/universe5010012
 | arxiv=1809.07568 | bibcode=2019Univ....5...12R 
| doi-access=free }}</ref>
* [[Radial-orbit instability]]
* Various instabilities{{which|date=December 2019}} in cold rotating disks