life cycle of stars

26.2

3/27/07

Star Stuff

Forming a StarNebulacloud of dust and gas

protostar(takes 50 million years)

Contracts and rotates to form a ________

A Star is Born!

•A star when ______ startsfusion

10

• Hydrogen atoms combine to form Helium, other atoms• Takes ___ billion years to form

Adult Stars•Called “main sequence” stars•Longest period in life cycle•How long depends on star mass

A Balancing Act• Two forces act on

stars•Outward force from energy released by nuclear fusion

•Inward force from gravity

Old Age• Hydrogen fusion

slows• Gravity contracts

core• Core temperature

rises• Helium fusion

starts, releasing even more energy

Small Stars

•Mass of our sun•Fusion forms Helium, some Lithium, Carbon and Oxygen

•Last up to ___ billion years10

Small Star Old Age Red Giant

• Helium fusion when H atoms used up– produces heavier atoms – carbon &

oxygen

• Temperature rises with Helium fusion• Outer layers expand• Lasts ____ million years100

Small Star Death

•Hydrogen & Helium used up

white dwarf

planetary nebula

• Outer layers expand to form a ________ _______• Star core cools and contracts to form a dim _____ _____

Large Stars•6 x mass of our sun, or more•Fusion forms Helium, some Lithium, Carbon, Oxygen and Iron

•Last up to ___ million years10

Old Massive Star SUPERGIANT!

•Can be 100 x larger than our sun

•Hydrogen used up•He fusion in core produces

heavier atoms•Finally, core made of Iron

Dying Large Stars•Hydrogen gone - fusion stops•Core collapses, then rebounds

with explosion•SUPERNOVA!•Lasts few seconds

After Supernova…

•If mass 1-3 x the sun, final stage is _______ ____neutron star

pulsar

dense

• Protons and electrons collapse together to form ________ neutrons• Very ______

• Called ______ if rotating

After Supernova 2…

•If mass > 3 x sun, final stage is _____ ____black hole

gravitydense

• Extreme ______• Very ______

• No light escapes from it