Life Cycle of a Star

What is a Star?

• 1. Giant balls of exploding gas consisting mainly of hydrogen and helium.

• 2. There are 100 billion stars in the Milky Way Galaxy alone

The Life Cycle of a Star Depends on its Mass

• 1. Nebula

• 2. Star/Large Star

• 3. Red Giant/Red Supergiant

• 4. Planetary Nebula/SuperNova

• 5. White Dwarf/ Blackhole/ Neutron Star

The Life Cycle Depends on Starting Mass Cont.

ProtostarMain SequenceWhite DwarfBlack Dwarf

ProtostarMain SequenceRed GiantWhite DwarfBlack Dwarf

ProtostarMain SequenceSuper GiantSupernova

neutron star black hole

Small Mass Medium Mass Large Mass

I: Stage One: a Nebula

• 1. All stars begin the same way

• 2. A nebula is a cloud of interstellar dust, hydrogen & helium gas, and plasma

II: Stage Two: The Protostar

• 1. Ball of gas and dust that is pulled together by gravity

III: Stage Three: Main Sequence

• 1. All stars go through a Main Sequence stage

• 2. Hydrogen fuses into helium which creates enormous amounts of energy (nuclear fusion)

• 3. Stars in the main sequence stage are middle aged stars

• 4. Longest stage

• 5. Luminosity (light) depends directly on temperature

IV: Stage Four: White Dwarf (Small Mass Star)

• 1. Small hot star that is the leftover center of an older star

• 2. Cooler & less bright than the main sequence star

IV: Stage Four: Red Giant (Medium Mass Star)

• 1. Occurs when star begins running out of hydrogen – it starts cooling and expanding at the same time

IV: Stage Four: Supergiant (Large Mass Star)

• 1. Occurs when star begins running out of hydrogen – it starts cooling and expanding at the same time

• 2. The only difference between a Red Giant and a Super Red Giant is the size and the luminosity

• 3. 1,000,000 times brighter than the sun

V: Stage Five: Black Dwarf (Small Mass Star)

• 1. A Black Dwarf is a White Dwarf that has cooled so much that it no longer emits heat or light

• 2. It is estimated that it takes more than 13 billion years for this to occur, so there are no black dwarfs around

V: Stage Five White Dwarf (Medium Mass Star)

• 1. Small hot star that is the leftover center of an older star

• 2. Cooler & less bright than the Red Giant

V: Stage Five: Supernova (Large Mass Star)

• 1. Gigantic explosion in which a massive star collapses after it uses up all its fuel

• 2. A Supernova explosion outshines an entire galaxy. It radiates as much energy as the Sun will emit over its entire life span

VI: Stage Six: Black Dwarf (Medium Mass Star)

• 1. A Black Dwarf is a White Dwarf that has cooled so much that it no longer emits heat or light

• 2. It is estimated that it takes more than 13 billion years for this to occur, so there are no black dwarfs around

VI: Stage Six: Neutron Star OR Black Hole (Large Mass Star)

• 2. Black Holes exhibit so much gravitational pull, that nothing can escape (including light rays)

• 1. Neutron Star- a star that has collapsed to a point at which all particles are neutrons1