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Life Cycle of Stars Chapter 21, section 3

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1 Life Cycle of Stars Chapter 21, section 3

2 2 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

3 3 Eagle Nebula /2009/01/hubble-eagle-nebula-wide-field-04086y.jpg Protostars images/158286.JPG

4 4 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

5 5 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.

6 6 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.

7 7 Life Cycle of a Star 1.Nebula/Protostar Small or Medium Star Giant or Supergiant Star Red Giant Supernova Black Dwarf Black HoleNuetron Star

8 8 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.

9 9 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.

10 10 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

11 11 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.

12 12 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

13 13 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

14 14 Medium-sized Star (The Sun)

15 15 Red Giants

16 16 Giants and Supergiants Red giant Supergiants

17 17 Supernova

18 18 White Dwarf and Black Dwarf NYC063368//blackdwarf.gif /images/screenshots/various/extrasolar_ stars_White_Dwarf_Sirius_B_1__ Frank_Gregorio.jpg

19 19 Neutron Star

20 20 Black Hole

21 21 Quasar DeepSpace/Quasars/Quasar3C273Hubble.jpg

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