Life Cycle of Stars
Chapter 21, section 3
http://www.freewebs.com/bnip1/Astronomy/Hidden%20Galaxy%20IC%20342.jpg
Nebulas and protostars
• A star is made up of a large amount of
gas in a relatively small volume.
• All stars begin as nebulas which are
large amounts of gas and dust spread
out over an immense (huge) volume.
• Gravity can pull some of the gas and
dust in a nebula together
• This contracting cloud is called a
protostar which is the earliest stage in
the life of a star
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Protostars
Eagle Nebula
http://feps.as.arizona.edu/outreach/
images/158286.JPG
http://larvalsubjects.files.wordpress.com
3
Birth of a Star
• A star is “born” when the
contracting gas and dust become
so hot that nuclear fusion begins
to occur.
• How long a star lives depends on
how much mass it has. Stars with
less mass burn their fuel more
slowly and last longer than stars
with more mass
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Lifetimes of Stars
• Stars with little mass can live as long
as 200 billion years.
• Stars that are 15 times bigger than the
sun might last only 10 million years.
• The sun is medium-sized and should
live for about 10 billion years, since the
sun is about 4.6 billion years old it is
almost halfway through its lifetime.
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Deaths of Stars
• When a star begins to run out of fuel,
the center of the star shrinks and the
outer part expands. The star becomes
a red giant or supergiant
• All main sequence stars eventually
become red giants or supergiants, what
happens next depends on the mass of
the star.
• When a star runs out of fuel it becomes
a white dwarf, a neutron star, or a black
hole.
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Life Cycle of a Star
Small or Medium Star
Black Dwarf
Red Giant
1.Nebula/Protostar
Giant or Supergiant Star
Supernova
Black Hole
Nuetron Star
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White Dwarfs
• Small- and Medium-sized stars
become red giants, then the outer
layers drift off into space. The
blue-white hot core is left behind
and is a white dwarf.
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and Black Dwarfs
• A White dwarf has the mass of the sun
but is the size of Earth, it is one million
times as dense as the sun. When a
white dwarf runs out of fuel and energy
it becomes a black dwarf.
• A black dwarf has stopped glowing
because fusion has stopped. It is a
“dead” star, not the Death Star that is
Darth Vader’s spacecraft.
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Neutron Stars
• Dying giant or supergiant stars can
explode, this is called a supernova.
Left behind is an incredibly dense
star called a neutron star, only
about 20 kilometers across.
• A spoonful of matter would have as
much mass as a large truck
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Black Holes
• Only the most massive stars with 40
times the mass of the sun become
black holes.
• After a supernova more than 5 times
the mass of the sun can be left.
• The gravity is so strong that gas is
pulled inward, eventually all of this
mass is contained with in a sphere
only 30 kilometers in diameter.
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Black Holes
• The gravity becomes so strong that
nothing can escape, not even light. This is
a black hole.
• No light, radio waves, or any form of
radiation can get out of a black hole.
Astronomers can not see black holes
directly.
• Astronomers can detect black holes
indirectly
– Gas pulled in rotates so fast that it heats up
and gives off X-rays
– Scientists can calculate the mass of a black
hole by it effect on nearby stars
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Quasars
• In the 1960’s astronomers
discovered very bright objects that
are very far away, about 12 billion
light-years away
• Astronomers concluded that
quasars are distant galaxies, each
with a black hole at its center
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Medium-sized Star (The
Sun)
http://www.physics.uci.edu/%7Eobservat/SunPluto.jpg
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Red Giants
http://www.physics.uci.edu/%7Eobservat/ArcturusSun.jpg 15
Giants and Supergiants
Supergiants
Red giant
http://www.physics.uci.edu/%7Eobservat/AntaresSun.jpg16
Supernova
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http://www.orionsarm.com/tech/supernova3.jpg
White Dwarf and Black
Dwarf
http://www.celestiamotherlode.net/catalog
/images/screenshots/various/extrasolar_
stars_White_Dwarf_Sirius_B_1__
Frank_Gregorio.jpg
http://www.tqnyc.org/2006/
18
NYC063368//blackdwarf.gif
Neutron Star
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http://www.ph.ed.ac.uk/nuclear/photo/xray_neutronstar.jpg
Black Hole
http://www.nrao.edu/images/supermassiveBlackHoleRip510.jpg20
Quasar
http://www.spacetoday.org/images/
DeepSpace/Quasars/Quasar3C273Hubble.jpg
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