What determines a star’s life cycle?

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The determining factor in a star's life cycle is its mass. A star's life cycle begins in a nebula. If there is a lot of matter available in the nebula, the star will have more opportunity to grow large. As hydrogen is pulled in gravity, a protostar may eventually gain...

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The determining factor in a star's life cycle is its mass. A star's life cycle begins in a nebula. If there is a lot of matter available in the nebula, the star will have more opportunity to grow large. As hydrogen is pulled in gravity, a protostar may eventually gain enough mass to begin the process of nuclear fusion. It will burn steadily as a main-sequence star as hydrogen is fused into helium within its core. Once the star runs out of hydrogen, it will begin cooling and expanding. As it cools, it will continue to expand and take on a red glow, becoming a red giant.

This is the phase in which a star's mass begins to matter. Low-mass stars will continue to cool as the helium core is gradually converted to carbon. It loses pull over its outer layers, which dissipate into space, forming a nebula. The core cools to a white dwarf and then to a black dwarf.

For stars with a lot of mass, they will explode as a supernova when the core begins fusing iron. Some of these will then end their life cycle as a neutron star. However, the stars with even more mass than this will go through further phases. If it is massive enough, the whole atomic structure of the core collapses in on itself, forming a black hole.

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