Chapter 21

1. Chapter 21 21.3 Lives of stars

2. Star Formation • All stars begin as a nebula- a large amount of gas spread out in an immense volume. • Gravity pulls the gas and dust together to form a protostar. (Earliest stage of a star’s life, it is not yet shining) • The star is born once nuclear fusion starts.

3. Lifetime of a star • How long a star lives depends only on how much mass it has. • The more mass (the bigger it is), the more quickly it will burn up its fuel. • The star is like a giant engine. The larger it is the faster it burns its fuel. Although a larger star has a larger gas tank, the engine can burn it up a much faster rate. For example, your car holds about 15 gallons of gas, and could run for a few hours even at top speed. The Space Shuttle has larger engines and burns up thousands of gallons in about 15 minutes.

4. Death of Stars • There are three fates that a star can have • White Dwarf • Neutron Star • Black Hole

5. Death of small to medium stars • When a medium or small star uses up its hydrogen fuel, it will start to fuse the newly made helium into carbon • Fusion of helium takes a much higher temperature, it heats the outer layers, and the star starts to expand • Our Sun will expand enough to swallow Mercury, venus, & the Earth

6. White Dwarf • Small to medium sized stars will become white dwarfs • Eventually the outer parts grow larger and drift out into space leaving only the white hot core. • White dwarfs are only about the size of the Earth, but contain as much mass as the Sun. A white dwarf has a very high density compared to the Earth.

7. Quasars • Are very distant galaxies that have a supermassive black hole (about a billion times more massive than our Sun) • The black holes have material spiraling into them. The material heats up to extreme temperatures causing them to burn brightly. • Because these quasars are far away, we are seeing what was happening to them billions of years ago when they were first forming.

8. Neutron Star • A dying giant star cam explode suddenly in what is called a supernova. • During a supernova a star can shine millions of times brighter. • The mater blown off into space can form a new nebula. • Gravity contracts the material left behind to an extremely dense mass. • A neutron star had at least 3 times the mass of the Sun and is squeezed into a sphere about 20 kilometers in diameter. (from about here to Doylestown)

9. Black Holes • The most massive stars that have about 40 times the mass of the Sun become black holes. • The mass is so great in such a small volume (The greatest density possible) that space is warped around the mass so much that nothing can escape from it once it crosses the event horizon- not even light.