Life Cycle of a Star

What happens to a star after the main sequence depends mainly on its mass.Main sequence. All stars spend most of their lives here, fusing hydrogen into helium in the core, with gravity balanced by outward pressure. More massive stars are hotter and more luminous, and use up their hydrogen much faster, so they have shorter main sequence lifetimes. The Sun will last about 10¹⁰ years; a star of 10 solar masses only about 10⁷ years.Low-mass stars (like the Sun):
• hydrogen in the core runs out, so the core contracts and heats up
• hydrogen fuses in a shell around the core and the outer layers expand and cool: the star becomes a red giant
• the core becomes hot enough to fuse helium into carbon and oxygen
• the outer layers drift away as a planetary nebula, leaving the hot core as a white dwarfHigh-mass stars (many times the Sun's mass):
• the star swells into a red supergiant
• the core fuses successively heavier elements, up to iron; fusing iron releases no energy
• the core collapses and the star explodes as a supernova, briefly outshining a whole galaxy and scattering heavy elements into space
• the remaining core becomes a neutron star or, for the most massive, a black holeOn the H-R diagram a star leaving the main sequence moves up and to the right into the giant region; a white dwarf ends at the bottom left.