24.2 - Life Cycle of Stars
The life cycle of a star
- Every star begins when an interstellar cloud of gas and dust (nebula) is pulled together by gravity.
- As the cloud collapses, it forms a hot, dense protostar.
- When the temperature and pressure are high enough, nuclear fusion begins, forming a stable main sequence star.
What happens next depends on mass
- A low-to-medium mass star (similar to the Sun) swells into a red giant, sheds its outer layers as a planetary nebula, and leaves behind a white dwarf.
- A massive star swells into a red supergiant, explodes as a supernova, and leaves behind a neutron star.
- A very massive star follows the same path - red supergiant then supernova - but its core collapses further into a black hole.
TermDefinition
NebulaA vast cloud of dust and gas in space.
ProtostarA cloud of gas and dust that is collapsing under gravity and heating up, before nuclear fusion has started.
Main sequenceThe long, stable stage of a star's life, when the inward pull of gravity is balanced by the outward push from nuclear fusion in its core.
Red giantA star that has swollen and cooled after running out of hydrogen in its core.
Planetary nebulaThe glowing shell of dust and gas thrown off by a red giant at the end of its life.
White dwarfThe small, hot, dense core left behind after a small-to-medium star has shed its outer layers.
Red supergiantA very large, cool star that a massive star swells into when the hydrogen in its core runs out.
SupernovaThe huge explosion of a star at the end of its life, such as a red supergiant whose core collapses.
Neutron starThe very small, extremely dense core left behind after a massive star explodes as a supernova.
Black holeAn extremely dense object with gravity so strong that not even light can escape it.