<P> The helium core of a red giant continues to collapse until it is entirely supported by electron degeneracy pressure--a quantum mechanical effect that restricts how closely matter can be compacted . For stars of more than about 0.5 M, the core eventually reaches a temperature where it becomes hot enough to burn helium into carbon via the triple alpha process . Stars with more than 5--7.5 M can additionally fuse elements with higher atomic numbers . For stars with ten or more solar masses, this process can lead to an increasingly dense core that finally collapses, ejecting the star's overlying layers in a Type II supernova explosion, Type Ib supernova or Type Ic supernova . </P> <P> When a cluster of stars is formed at about the same time, the life span of these stars will depend on their individual masses . The most massive stars will leave the main sequence first, followed steadily in sequence by stars of ever lower masses . Thus the stars will evolve in order of their position on the main sequence, proceeding from the most massive at the left toward the right of the HR diagram . The current position where stars in this cluster are leaving the main sequence is known as the turn - off point . By knowing the main sequence lifespan of stars at this point, it becomes possible to estimate the age of the cluster . </P>

Main sequence stars have radii ranging from about 0.03 solar radius to 30 solar radius