Lives of Stars

1. Lives of Stars Chapter 3 Lesson 5 Page 116

2. How Does a Star Form? • Stars do not last forever • Each star goes through a life cycle like we do (not literally, but a general comparison) • A star is born when the contracting gas and dust from a nebula become so dense and hot that nuclear fusion starts. How long a star lives depends on its mass.

3. A Star is Born • All stars begin as parts of a nebula • Nebula- a large cloud of gas and dust spread out in an immense volume • A star is a is a large amount of gas in a relatively small volume • In the densest part of the nebula gravity pulls gas and dust together • Protostar- a contracting cloud of gas and dust with enough mass to form a star (proto-first)

4. A Star is Born • Nuclear Fusion- the combining of atoms to create heavier atoms • During nuclear fusion, enormous amounts of energy are released • Nuclear fusion begins a protostar

5. Lifetimes of Stars • How long a star lives depends on the star’s mass • The smaller mass stars have longer lives than larger mass stars • Read page 118 • Some can live up to 200 billion years! • Medium mass stars will live around 10 billion years • Many blue stars only live around 10 million years

6. What happens when stars run out of Fuel? • When a star begins to run out of fuel its core shrinks and other portions expand • Depending on its mass, it will become a red giant or a supergiant • Red giants and super giants evolve in very different ways • After a star runs out of fuel, it becomes a white dwarf, a neutron, or a black hole

7. White Dwarf • Low-mass stars and medium-mass stars like the sun take billions of years to use up their fuel • As they start to run out, their outer layers expand and they become red giants • The outer part grow large and drift out into space forming a cloud called a planetary nebula • The blue-white core is left behind and cools becoming a white-dwarf

8. White Dwarf • White Dwarf- the blue-white core of the star that is left behind and cools • About the size of Earth, but have as much mass as the sun • They have no fueland glow faintly • After billions of years they stop glowing and become black dwarfs

9. Supernovas • Life cycle of a high mass (large) star is different • When a supergiant runs out of fuel is can explode suddenly • The star is will blaze millions of times brighter • Supernova- the explosion of a supergiant • Some of the material can expand into space becoming a nebula which can turn into a new star • Supernovas provide enough energy to create the heaviest elements • This is what scientists believe created the sun, Earth and everything in space

10. Neutron Stars • Neutron Stars- the remains of high-mass stars • Smaller and denser than white dwarfs • Can contain 3x’s the amount of mass as the sun! • Read 2nd paragraph page 120 • Pulsars- rapidly spinning neutron stars that give off radio waves

11. Black Holes • Most massive star may become black holes when they die • Black hole- an object with gravity so strong that not even light can escape • After a supernova explosion, a large amount of mass is left behind • The gravity of this mass is so strong that gas is pulled inward, packing the gas into smaller and smaller space

12. Black Hole • The gas is squeezed so hard that it becomes the black hole • No light, radio waves, or any other form of radiation can escape • Hard to detect, but they can tell it is there indirectly • Gas that is pulled in is pulled so hard it starts to revolve around faster and faster around the black hole • Friction heats up the gas which causes it to x-rays which is what astronomers can detect