Editing Globular cluster (section)

===Consequences===
The blue stragglers appear on the H–R diagram as a series diverging from the main sequence in the direction of brighter, bluer stars.<ref name=":0" /> [[White dwarf]]s (the final remnants of some Sun-like stars), which are much fainter and somewhat hotter than the main-sequence stars, lie on the bottom-left of an H–R diagram. Globular clusters can be dated by looking at the temperatures of the coolest white dwarfs, often giving results as old as 12.7 [[1000000000 (number)|billion]]<!--The 1,000,000,000 link is to clarify the ambiguity of the term "billion". Please do not change it.--> years.<ref>{{cite journal
 |author1=Hansen, B. M. S. |author2=Brewer, J. |author3=Fahlman, G. G. |author4=Gibson, B. K. |author5=Ibata, R. |author6=Limongi, M. |author7=Rich, R. M. |author8=Richer, H. B. |author9=Shara, M. M. |author10=Stetson, P. B. | title=The White Dwarf Cooling Sequence of the Globular Cluster Messier 4
 | date=2002 | journal=Astrophysical Journal Letters
 | volume=574
 | issue=2 | pages=L155
 | arxiv=astro-ph/0205087 | doi=10.1086/342528 | bibcode=2002ApJ...574L.155H|s2cid=118954762 }}</ref> In comparison, open clusters are rarely older than about half a billion years.<ref>{{cite journal |last1=Soderblom |first1=David R. |title=The Ages of Stars |journal=Annual Review of Astronomy and Astrophysics |date=August 2010 |volume=48 |issue=1 |pages=581–629 |doi=10.1146/annurev-astro-081309-130806 |bibcode=2010ARA&A..48..581S |arxiv=1003.6074|s2cid=119102781 }}</ref> The ages of globular clusters place a lower bound on the age of the entire universe, presenting a significant constraint in [[Physical cosmology|cosmology]]. Astronomers were historically faced with age estimates of clusters older than their cosmological models would allow,<ref>{{cite journal |doi=10.1086/187847 |title=Absolute ages of globular clusters and the age of the universe |year=1995 |last1=Chaboyer |first1=Brian |journal=The Astrophysical Journal |volume=444 |pages=L9 |arxiv=astro-ph/9412015 |bibcode=1995ApJ...444L...9C |s2cid=2416004 }}</ref> but better measurements of cosmological parameters, through deep sky surveys and satellites, appear to have resolved this issue.<ref>{{cite journal |doi=10.1088/1475-7516/2020/12/002 |title=Inferring the age of the universe with globular clusters |year=2020 |last1=Valcin |first1=David |last2=Bernal |first2=José Luis |last3=Jimenez |first3=Raul |last4=Verde |first4=Licia |last5=Wandelt |first5=Benjamin D. |journal=Journal of Cosmology and Astroparticle Physics |volume=2020 |issue=12 |page=002 |arxiv=2007.06594 |bibcode=2020JCAP...12..002V |s2cid=220514389 }}</ref><ref>{{cite news
 |author=Majaess, D.
 |date=February 23, 2013
|title=Nearby Ancient Star is Almost as Old as the Universe
 |url=http://www.universetoday.com/100147/nearby-ancient-star-is-almost-as-old-as-the-universe/
 |work=Universe Today
 |access-date=November 29, 2014 }}</ref>

Studying globular clusters sheds light on how the composition of the formational gas and dust affects stellar evolution; the stars' [[evolutionary track]]s vary depending on the abundance of heavy elements. Data obtained from these studies are then used to study the evolution of the Milky Way as a whole.<ref name="ashes">{{cite press release |url=http://www.eso.org/public/news/eso0107/ |publisher=[[European Southern Observatory]] |date=March 2, 2001 |title=Ashes from the Elder Brethren |access-date=April 7, 2021 | id=eso0107}}</ref>