Editing Ring galaxy (section)

{{short description|Galaxy with an annular appearance}}
[[Image:Hoag's object.jpg|right|thumb|[[Hoag's Object]], a ring galaxy. Another red ring galaxy can be seen behind it.]]

A '''ring galaxy''' is a [[galaxy]] with a circle-like appearance. [[Hoag's Object]], discovered by [[Arthur Hoag]] in 1950, is an example of a ring galaxy.<ref name=APOD>{{Cite APOD|title=Hoag's Object: A Strange Ring Galaxy|date=September 9, 2002|access-date=March 31, 2012}}</ref> The ring contains many massive, relatively young blue [[star]]s, which are extremely bright. The central region contains relatively little luminous [[matter]]. Some [[astronomer]]s believe that ring galaxies are formed when a smaller galaxy passes through the center of a larger galaxy. Because most of a galaxy consists of empty space, this "collision" rarely results in any actual collisions between stars. However, the [[gravity|gravitational]] disruptions caused by such an event could cause a [[wave]] of star formation to move through the larger galaxy.<ref>{{Cite journal |last=Fernandez |first=Julia |last2=Alonso |first2=Sol |last3=Mesa |first3=Valeria |last4=Duplancic |first4=Fernanda |last5=Coldwell |first5=Georgina |date=2021-09-01 |title=Properties of galaxies with ring structures |url=https://www.aanda.org/articles/aa/full_html/2021/09/aa41208-21/aa41208-21.html |journal=Astronomy & Astrophysics |language=en |volume=653 |pages=A71 |doi=10.1051/0004-6361/202141208 |issn=0004-6361|arxiv=2107.06920 }}</ref> Other astronomers think that rings are formed around some galaxies when external [[Accretion (astrophysics)|accretion]] takes place. Star formation would then take place in the accreted material because of the shocks and compressions of the accreted material.<ref>{{Cite web|url=http://ned.ipac.caltech.edu/level5/Sept01/Appleton/frames.html|title=Collisional Ring Galaxies|first1=P.N.|last1=Appleton|first2=Curtis|last2=Struck-Marcell|year=1996|access-date=March 31, 2012}}</ref><ref>{{Cite web |date=2022-04-20 |title=Ring galaxies, the rarest in the Universe, finally explained |url=https://bigthink.com/starts-with-a-bang/ring-galaxies/ |access-date=2024-09-13 |website=Big Think |language=en-US}}</ref>