Earth & Beyond
Birth and death of stars, galaxies, universe
Birth and Death of Stars
Stars form in nebulae (clouds of gas and dust). Gravity pulls gas together until nuclear fusion begins — hydrogen fuses to form helium, releasing enormous energy. A star's life depends on its mass.
Example
Stellar Life Cycle
Medium star: Nebula -> Protostar -> Main sequence star (like our Sun) -> Red giant -> White dwarf. Massive star: Nebula -> Protostar -> Main sequence -> Red supergiant -> Supernova -> Neutron star or Black hole.
Note
Key Point
All elements heavier than helium were created inside stars or during supernovae. The atoms in your body were once inside a star. The universe began with the Big Bang approximately 13.8 billion years ago.
Key Vocabulary
NebulaA large cloud of gas and dust in space where stars are born
Nuclear fusionA reaction where atomic nuclei combine, releasing enormous energy
SupernovaA massive explosion that occurs when a large star dies
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Nebula
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