Editing Star cluster (section)

==Intermediate forms==
[[File:A Ten Billion Year Stellar Dance.jpg|thumb|[[Messier 68]], a loose [[globular cluster]] whose constituent stars span a volume of space more than a hundred light-years across]]

In 2005, astronomers discovered a new type of star cluster in the Andromeda Galaxy, which is, in several ways, very similar to globular clusters although less dense. No such clusters (which also known as ''extended globular clusters'') are known in the Milky Way. The three discovered in [[Andromeda Galaxy]] are [[M31WFS C1]]<ref>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=@1592523&M31WFS+C1|title=@1592523|website=u-strasbg.fr|access-date=28 April 2018}}</ref> [[M31WFS C2]], and [[M31WFS C3]].

These new-found star clusters contain hundreds of thousands of stars, a similar number to globular clusters. The clusters also share other characteristics with globular clusters, ''e.g.'' the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across – and hundreds of times less dense. The distances between the stars are thus much greater. The clusters have properties intermediate between globular clusters and [[dwarf spheroidal galaxy|dwarf spheroidal galaxies]].<ref name="extended">{{cite journal|author=A. P. Huxor|author2=N. R. Tanvir|author3=M.J. Irwin|author4= R. Ibata|title=A new population of extended, luminous, star clusters in the halo of M31|journal=[[Monthly Notices of the Royal Astronomical Society]]|date=2005|volume= 360|issue=3|pages=993–1006|arxiv=astro-ph/0412223|doi=10.1111/j.1365-2966.2005.09086.x|doi-access=free |bibcode=2005MNRAS.360.1007H|s2cid=6215035}}</ref>

How these clusters are formed is not yet known, but their formation might well be related to that of globular clusters. Why M31 has such clusters, while the Milky Way has not, is not yet known. It is also unknown if any other galaxy contains this kind of clusters, but it would be very unlikely that M31 is the sole galaxy with extended clusters.<ref name="extended"/>

Another type of cluster are ''faint fuzzies'' which so far have only been found in [[lenticular galaxy|lenticular galaxies]] like [[NGC 1023]] and [[NGC 3384]]. They are characterized by their large size compared to globular clusters and a ringlike distribution around the centres of their host galaxies. As the latter they seem to be old objects.<ref name="faintfuzzies">{{cite journal|author=A. Burkert|author2=J. Brodie |author3=S. Larsen 3|title=Faint Fuzzies and the Formation of Lenticular Galaxies|journal=The Astrophysical Journal|date=2005|volume= 628|issue=1|pages=231–235|arxiv=astro-ph/0504064|doi=10.1086/430698|bibcode=2005ApJ...628..231B|s2cid=11466131 }}</ref>