2Nebulas 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 togetherThis contracting cloud is called a protostar which is the earliest stage in the life of a star
4Birth of a StarA 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
5Lifetimes of StarsStars 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.
6Deaths of StarsWhen 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 supergiantAll 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.
7Life Cycle of a Star White Dwarf Black Dwarf Small or Medium Star Red Giant1.Nebula/ProtostarGiant or Supergiant StarSupernovaBlack HoleNuetron Star
8White DwarfsSmall- 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.
9and Black Dwarfs White 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.
10Neutron StarsDying 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
11Black HolesOnly 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.
12Black HolesThe 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 indirectlyGas pulled in rotates so fast that it heats up and gives off X-raysScientists can calculate the mass of a black hole by it effect on nearby stars
13QuasarsIn the 1960’s astronomers discovered very bright objects that are very far away, about 12 billion light-years awayAstronomers concluded that quasars are distant galaxies, each with a black hole at its center