Editing Globular cluster (section)

===Intermediate forms===
[[File:Globular Cluster M10.jpg|thumb|alt=Thousands of white-ish dots scattered on a black background, strongly concentrated towards the center|[[Messier 10]] lies about 15,000 light-years from Earth, in the constellation of [[Ophiuchus (constellation)|Ophiuchus]].<ref>{{cite news|title=Globular Cluster M10|url=http://www.spacetelescope.org/images/potw1225a/|access-date=June 18, 2012|newspaper=ESA/Hubble Picture of the Week}}</ref>]]

Cluster classification is not always definitive; objects have been found that can be classified in more than one category. For example, BH 176 in the southern part of the Milky Way has properties of both an open and a globular cluster.<ref>{{cite journal | last1=Ortolani |first1=S. |last2=Bica |first2=E. |last3=Barbuy |first3=B.
 | title=BH 176 and AM-2: globular or open clusters? | journal=Astronomy and Astrophysics | date=1995 | volume=300 | page=726 | bibcode=1995A&A...300..726O}}</ref>

In 2005 astronomers discovered a new, "extended" type of star cluster in the Andromeda Galaxy's halo, similar to the globular cluster. The three new-found clusters have a similar star count to globular clusters and share other characteristics, such as stellar populations and metallicity, but are distinguished by their larger size{{snd}}several hundred light years across{{snd}}and some hundred times lower density. Their stars are separated by larger distances; parametrically, these clusters lie somewhere between a globular cluster and a [[dwarf spheroidal galaxy]].<ref name="extended">{{cite journal
 |author1=Huxor, A. P. |author2=Tanvir, N. R. |author3=Irwin, M. J. |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>
The formation of these extended clusters is likely related to accretion.<ref>{{cite journal |last1=Huxor |first1=A. P. |last2=Mackey |first2=A. D. |last3=Ferguson |first3=A. M. N. |last4=Irwin |first4=M. J. |last5=Martin |first5=N. F. |last6=Tanvir |first6=N. R. |last7=Veljanoski |first7=J. |last8=McConnachie |first8=A. |last9=Fishlock |first9=C. K. |last10=Ibata |first10=R. |last11=Lewis |first11=G. F. |title=The outer halo globular cluster system of M31 – I. The final PAndAS catalogue |journal=Monthly Notices of the Royal Astronomical Society |date=August 11, 2014 |volume=442 |issue=3 |pages=2165–2187 |doi=10.1093/mnras/stu771|doi-access=free |arxiv=1404.5807 }}</ref> It is unclear why the Milky Way lacks such clusters; Andromeda is unlikely to be the sole galaxy with them, but their presence in other galaxies remains unknown.<ref name="extended" />