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Life Cycle of StarsChapter 21, section 3
http://www.freewebs.com/bnip1/Astronomy/Hidden%20Galaxy%20IC%20342.jpg
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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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Eagle Nebula
http://larvalsubjects.files.wordpress.com/2009/01/hubble-eagle-nebula-wide-field-04086y.jpg
Protostars
http://feps.as.arizona.edu/outreach/images/158286.JPG
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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
1.Nebula/ProtostarSmall or Medium Star
Giant or Supergiant Star
Red Giant
Supernova
Black Dwarf
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
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Giants and Supergiants
http://www.physics.uci.edu/%7Eobservat/AntaresSun.jpg
Red giant
Supergiants
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Supernova
http://www.orionsarm.com/tech/supernova3.jpg
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White Dwarf and Black Dwarf
http://www.tqnyc.org/2006/NYC063368//blackdwarf.gif
http://www.celestiamotherlode.net/catalog/images/screenshots/various/extrasolar_stars_White_Dwarf_Sirius_B_1__Frank_Gregorio.jpg
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Neutron Star
http://www.ph.ed.ac.uk/nuclear/photo/xray_neutronstar.jpg
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Black Hole
http://www.nrao.edu/images/supermassiveBlackHoleRip510.jpg
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Quasar
http://www.spacetoday.org/images/DeepSpace/Quasars/Quasar3C273Hubble.jpg