Chapter 19-2

Life Cycle of Stars

The Beginning of StarsBall of gas and dustGravity pulls the gas and dust together into

a sphereAs density increases, so does the

temperatureHydrogen changes to helium (nuclear

fusion)

Main SequenceThe second and longest stage of its life

cycleDuring this time,

nuclear fusion releases enormous amount of energy

the size changes very little

Red GiantsA large, reddish star late (3rd stage) in its

life cycleCreated when hydrogen is “used up”,

which causes:the core to shrinkthe atmosphere to become largethe star to cool

Can be 10 or more times biggerthan our sun

Red SupergiantsForm the same way as red giantsAre at least 100 times bigger than the sun

White DwarfsA small, hot, dim star that is the leftover

center of an old starCan shine for billions of years before

cooling off completely

Average Stars Larger StarsMain Sequence

Red Giants

White Dwarfs

Main Sequence

Red Supergiants

Supernova

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SupernovaA gigantic explosion in which a massive

star collapses and throws its outerlayers into space

• Comes from massive blue star• Can be brighter than an entire

galaxy

Leftovers of SupernovaNeutron Stars and

PulsarsBlack Holes

Neutron Stars and PulsarsNeutron Star: a star that has collapsed

under gravity to the point that the electrons and protons have smashed together to form neutronsComes from the materials in the center of a

supernova being squeezed together

Pulsar: a rapidly spinning neutron star that emits rapid pulses of radio and optical energy

Black HolesForms when the leftovers of a supernova

are incredibly massiveBlack Hole: an object so massive and

dense that even light cannot escape its gravity

H-R diagram