1. DO NOW QUESTION What life stage is our Sun currently in? What do you think will happen to our Sun as it gets older?

3. The Life Cycle of Stars

4. Stage 1: Formation  Enters first stage as a ball of gas and dust  Gravity pulls the gas and dust together into a sphere  As the sphere becomes denser, it gets hotter and the hydrogen changes into helium

6. Stage 2: Main Sequence  The longest stage  In the core of this type of star, hydrogen atoms fuse into helium atoms releasing a huge amount of energy

7. Nuclear Fusion  Occurs when hydrogen changes to helium  This process releases energy that fuels the star 2 hydrogen atoms combine 1 helium atoms is produced 1 hydrogen atom 1 hydrogen atom + energy is released

8. Stage 3: Red Giant  The star expands and cools once it uses all of its hydrogen  The center of the star shrinks  The star’s atmosphere then grows very large and cools  The star is reddish in color Red giants size comparison to our Sun. Note, red giants can vary in size.

9. Stage 4: White Dwarf  Final stage of a star’s life cycle  Has the same mass as the sun or smaller  A small hot star that is the leftover center of an older stare  There is no hydrogen left and can no longer generate energy by fusing hydrogen atoms into helium atoms About the same size as Earth

10. Supernova  At the end of its life, a massive star may explode in a large, bright flash called a supernova  A gigantic explosion in which a massive star collapses and throws its outer layers into space Chandra, Hubble, and Spitzer Space Telescope image of Crab Nebula supernova remnant

11. Neutron Star  Following a supernova, the center of the collapsed star contracts to form a neutron star  A star that has collapsed under gravity to the point at which all of the stars particles are neutrons

12. Pulsar  A spinning neutron star that sends out radiation across space  This radiation (radio waves) is detected on Earth by radio telescopes Vela pulsar, picture taken by Chandra X-Ray Observatory

13. Black Hole  An object that is so massive that light cannot escape  If the center of a collapsed star has a mass that is more than 3 times the mass of the sun, the star may contract further because of gravity  The force of the contractions crushes the dense center of the star and leaves a black hole