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The most massive stars do not become red giants; instead, their cores quickly become hot enough to fuse helium and eventually heavier elements and they are known as [[supergiant]]s. They follow approximately horizontal evolutionary tracks from the main sequence across the top of the H–R diagram. Supergiants are relatively rare and do not show prominently on most H–R diagrams. Their cores will eventually collapse, usually leading to a [[supernova]] and leaving behind either a [[neutron star]] or [[black hole]].<ref name=sitko00>{{cite web |last=Sitko |first=Michael L. |date=24 March 2000 |url=http://www.physics.uc.edu/~sitko/Spring00/4-Starevol/starevol.html |title=Stellar Structure and Evolution |publisher=University of Cincinnati |access-date=2007-12-05 |archive-url=https://web.archive.org/web/20050326090756/http://www.physics.uc.edu/~sitko/Spring00/4-Starevol/starevol.html |archive-date=26 March 2005}}</ref>
When a [[star cluster|cluster of stars]] is formed at about the same time, the main-sequence lifespan of these stars will depend on their individual masses. The most massive stars will leave the main sequence first, followed in sequence by stars of ever lower masses. The position where stars in the cluster are leaving the main sequence is known as the [[turnoff point]]. By knowing the main-sequence lifespan of stars at this point, it becomes possible to estimate the age of the cluster.<ref name=science299_5603>{{cite journal |last=Krauss |first=Lawrence M. |author2=Chaboyer, Brian |title=Age Estimates of Globular Clusters in the Milky Way: Constraints on Cosmology |journal=Science |date=2003 |volume=299 |issue=5603 |pages=65–69 |doi=10.1126/science.1075631 |pmid=12511641 |bibcode=2003Sci...299...65K |s2cid=10814581
==See also==
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<ref name=asr34_1>{{cite journal |last=Gloeckler |first=George |author2=Geiss, Johannes |title=Composition of the local interstellar medium as diagnosed with pickup ions |journal=Advances in Space Research |date=2004 |volume=34 |issue=1 |pages=53–60 |bibcode=2004AdSpR..34...53G |doi=10.1016/j.asr.2003.02.054}}</ref>
<ref name=science293_5538>{{cite journal |last=Schilling |first=Govert |title=New Model Shows Sun Was a Hot Young Star |journal=Science |date=2001 |volume=293 |issue=5538 |pages=2188–2189
<ref name=zams_sao>{{cite encyclopedia |url=https://astronomy.swin.edu.au/cosmos/Z/Zero+Age+Main+Sequence |title=Zero Age Main Sequence |encyclopedia=The SAO Encyclopedia of Astronomy |publisher=Swinburne University |access-date=2007-12-09}}</ref>
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