1. THE LIFE CYCLE OF STARS This star has entered the last stage of its life cycle

2. The first stage of star formation is NUCLEAR FUSION Gravity pulls clouds ofgas and dust (nebulae) together into a sphere – as it becomes denser, it gets hotter and the hydrogen changes to helium.

3. Stars are classified by: 1.Size 2.Brightness 3.Mass 4.Color 5.Temperature 6.Spectrum 7.Age

4. TYPES OF STARS : MAIN SEQUENCE STARS – this is the second phase and the longest phase Energy is generated in the core as hydrogen atoms fuse into helium atoms Stars are about 98% Hydrogen and Helium The sun in this stage (10 million yrs. to become this stage – has been shining for 5 billion years ) Earth is 4.6 billion years old

5. GIANTS AND SUPERGIANTS Third stage – RED GIANT RED GIANT – A large reddish star late in its life cycle - a star that expands and cools once it uses all of its hydrogen Eventually will shrink When shrinks – atmosphere grows large and cools to a red giant or red supergiant In 5 billion years the sun will become a red giant

6. Red giants – 10 or more times bigger than the sun. Red Supergiants – at least 100 times bigger than the sun.

7. WHITE DWARFS AND RED DWARFS WHITE DWARF – a small, hot, dim star that is the leftover center of an old star No hydrogen left Can shine for billions of years before they cool completely RED DWARF – low-mass stars Oldest stars in the universe

8. BLUE STARS BLUE STARS – very massive blue stars are not in the main sequence very long. They quickly use up the hydrogen in their cores Expand and turn into giants or supergiants

9. SUPERNOVAS A main sequence star with a mass of more than about 10 Suns experiences a spectacular end. It swells into a red supergiant with cooling, expanding outer layers. Eventually its core collapses, causing a huge explosion known as a supernova

10. A gigantic explosion in which a massive star collapses and throws its outer layers into space

11. NEUTRON STARS and PULSARS NEUTRON STAR – a star that has collapsed under gravity to the point that the electrons and protons have smashed together to form neutrons If the core of a supernova has relatively low mass, the core will be crushed into a tiny, super dense neutron star PULSAR – a spinning neutron star

12. BLACK HOLE A volume of space in which gravity is SO GREAT that nothing can escape, not even light, although objects can fall in If the core of a supernova has a mass of more than about two Suns, its own gravity will squash it further, into a black hole.

13. HR Diagram (page 592 – 593) Shows the relationship between a star’s surface temperature and absolute magnitude.

14. Hertzsprung-Russell Diagram The temperature is given along the bottom of the diagram.

15. Hertzsprung-Russell Diagram The absolute magnitude (brightness) is given along the left side.

16. Hertzsprung-Russell Diagram The Hot (blue) stars are located on the LEFT The Cool (red) stars are located on the RIGHT.

17. Hertzsprung-Russell Diagram The BRIGHT stars are at the TOP. The DIM stars are at the BOTTOM.

20. The DIAGONAL pattern where most stars lie is the MAIN SEQUENCE. The SUN is located in the middle of the diagram. Average stars like the sun become giants or supergiants (Right) and then down to the left to become white dwarfs.