Editing Ring galaxy (section)

===Galactic collisions===

Another observed way that ring galaxies can form is through the process of two or more galaxies colliding. The [[Cartwheel Galaxy]], galaxy pair [[AM 2026-424]], and [[Arp 147]] are all examples of ring galaxies thought to be formed by this process.<ref name=":0" /> 

In pass-through galactic collisions, or bullseye collisions, an often smaller donor galaxy will pass directly through the disc of an often larger spiral, causing an outward push of the arms from the gravity of the smaller galaxy, as if dropping a rock into a pond of still water. These collisions can either launch the bulge and core away from the main disk, creating an almost empty ring appearance as the shockwave pushes the spiral arms out, or shove the core out towards the disk, often creating an oval-shaped ring with the bulge still somewhat intact.<ref>{{Cite journal |last=Theys |first=J. C. |last2=Spiegel |first2=E. A. |date=1976-09-01 |title=Ring galaxies. I. |url=https://ui.adsabs.harvard.edu/abs/1976ApJ...208..650T/abstract |journal=The Astrophysical Journal |volume=208 |pages=650–661 |doi=10.1086/154646 |issn=0004-637X |via=Astrophysics Data System}}</ref> In side-swipe and head-on collisions, the appearance of a perfect ring are less likely, with chaotic and warped appearances dominating. In these collisional galaxy systems, the individual galaxies that made up the ring system are often still observable.<ref name=":0" /> 

Rings formed through collision processes are believed to be transient features of the affected galaxies, lasting only a few ten to hundred million years (a relatively short timeframe considering some mergers can take over a billion years to complete) before disintegrating, reforming into spiral arms, or succumbing to further disturbance from gravitational influence.<ref>{{Cite journal |last=Theys |first=J. C. |last2=Spiegel |first2=E. A. |date=1977-03-01 |title=Ring galaxies. II. |url=https://ui.adsabs.harvard.edu/abs/1977ApJ...212..616T/abstract |journal=The Astrophysical Journal |volume=212 |pages=616–619 |doi=10.1086/155084 |issn=0004-637X |via=Astrophysics Data System}}</ref>