Life Cycle of a Life Cycle of a StarStar
All Stars Begin the Same All Stars Begin the Same Way:Way:
Before life as a star Nebula
A nebula is a cloud of interstellar dust, hydrogen and helium gas, and plasma
All Stars Begin the Same All Stars Begin the Same Way:Way:
1st Stage of Life – the Protostar
Ball of gas and dust that is pulled together by gravity
Nuclear fusion starts as gas cloud becomes denser and hotter
Nuclear Fusion hydrogen atoms fuse into helium
Creates the intense energy found in stars
The Life Cycle Depends The Life Cycle Depends on Starting Masson Starting Mass
ProtostarMain SequenceWhite DwarfBlack Dwarf
ProtostarMain SequenceRed GiantWhite DwarfBlack Dwarf
ProtostarMain SequenceSuper GiantSupernova
neutron star black hole
Small Mass Medium Mass Large Mass
Main Sequence StageMain Sequence Stage
longest stage
hydrogen fuses into helium which creates enormous amounts of energy (nuclear fusion)
the size of the star does not change much
this is the stage our sun is currently in
“middle age”
Main Sequence StageMain Sequence Stage
Remember, all stars go through a main sequence stage
Large Mass stars = large main sequence stars
Medium Mass stars = medium-sized main sequence stars
Red GiantsRed Giants
Red GiantsRed Giants
This Stage Happens for Medium Mass Stars Onlyoccurs when star begins running out of hydrogen – it starts cooling and expanding at the same timecenter shrinks and atmosphere swells
Red GiantsRed Giants
the end of the red giant stage occurs when the atmosphere of the star becomes so spread out it slowly dissipates
this stage is called “planetary nebula”
Red GiantsRed Giants
planetary nebulawhite dwarf
White DwarfsWhite Dwarfs
White Dwarf small hot star that is the leftover center of an older star
Can shine for billions of years before they extinguish
White DwarfsWhite Dwarfs
SupergiantsSupergiants
Stage That Happens For Large Mass stars only
occurs when star begins running out of hydrogen – it starts cooling and expanding at the same time
center shrinks and atmosphere swells
looks a lot like a red giant, doesn’t it?
SupergiantsSupergiants
the big difference is thesizeand brightness
supergiants are up to 1,000,000 times brighter than the sun
medium star
Jupiter
large mass star
Relative Size of StarsRelative Size of Stars
Giant stars
SupernovaSupernovaSupernova
gigantic explosion in which a massive star collapses
occurs after a massive star uses up its fuel source
supernova
Neutron Star
Neutron Star
A neutron star that spins and sends out beams of radiation is called a pulsar
a star that has collapsed to a point at which all particles are neutrons
Black HoleBlack Hole
Black Hole
an object that is so massive that light cannot escape its gravity
Astronomers can detect black holes by using X-ray telescopes
Neutron Star or Black Neutron Star or Black Hole?Hole?
Black Hole Neutron Star
~ 8 to 15 solar masses > 15 solar masses
SummarySummary
Observe life of a star
Recall:
Comprehend:
Apply:
S T A R
S
S
T
T
A
A
R
R
What is the longest stage for any star?
All stars remain in their Main Sequence stage longer than in any other stage
What are neutron stars made of?
Neutron stars are made of neutrons. A neutron star is so dense that a teaspoonful would weigh 1 billion tons!
What kind of stars form a supernova?
Only large mass stars form supernova.
What kind of stars form red giants?
Medium mass stars like our sun form red giants.
What size of stars will form black holes?
Only stars with 15 solar masses or larger will form black holes.
What kind of stars “skip” the red giant /supergiant phase altogether?
Small mass stars go straight from their main sequence stage to white dwarf
What stages do all stars have in common?
All stars begin as nebula, become protostars and then become main sequence stars.
What kind of stars are smaller than Earth?
Both white dwarfs and neutron stars are smaller than Earth.
What is the one factor that determines the ultimate fate of a star?
The mass of a star determines its fate.
Which main sequence stars are larger than the Earth?
All main sequence stars are larger than Earth.
Why won’t our sun ever become a black hole?
Our sun will never become a black hole because it does not have enough mass.
How many times larger would our sun have to be to supernova?
It takes a star that is at least 8 solar masses to be massive enough to supernova, so our sun would have to be at least 8 times as large.
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