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