1. Star Types & Life Cycle of a Star

2. Types of Stars 2 Factors determine a Star’s Absolute Brightness: 1.Size of Star and 2. Surface Temperature of Star Supergiants: Upper Right of H-R Diagram Much Brighter than Main Sequence Stars at Same Temperature 100-1000x size of the Sun Must be Extremely Large to Be So Bright!

3. Giants: Just below the Supergiants Large, Bright Stars that are smaller and fainter (dimmer ) than supergiants White Dwarfs: Lower Left of H-R Diagram (below the Main Sequence) Small dense remains of a Low/Medium Mass Star Hot, but dimmer than Main Sequence stars at Same Temp

4. Make Note: Using the H-R Diagram, you can Compare Stars at the Same Temperature~~ *Brighter ones will be Larger Also, Hotter Stars are Brighter than Cooler Stars at the Same Size

5. 26.3 Life Cycles of Stars For Most of a Star’s Life---they are very Stable. But a Star must change when nuclear fusion has used the supply of Hydrogen in its Core.

6. Star Formation A star begins as a large cloud of gas and dust called a NEBULA. A strong gravity develops and the nebula begins to contract, which means the particles in the cloud move closer together. A PROTOSTAR forms. This causes the temperature to Increase.

7. Next…. Once the Temperature reaches 10,000,000 degrees C, fusion begins and energy in the form of light and heat is given off. = A STAR IS BORN! The Pressure Created from Fusion and the Force of Gravity makes the Star Stable. The Star Becomes a MAIN SEQUENCE STAR.

8. Death of a Star Dwindling Supply of Fuel in a Star’s Core Ultimately leads to the Star’s death as a White Dwarf, Neutron Star, or Black Hole! Over Time, the Hydrogen fuel gets used up. There is no longer a balance between Pressure and Gravity. The Core contracts and the outer layers of the Star begin to Expand~~It is Now a GIANT.

9. **Our Sun will become a Giant in about 5 billion years. Later it will become a White Dwarf and then a Black Dwarf. White Dwarf: As dying star blows off its mass, a Hot Core remains, this dense core is called a white dwarf. When a white dwarf Becomes too Cool to Glow---it is then called a Black Dwarf. (Note: It takes 20 billion years to cool down, SO our Universe has NOT been here long enough to form any Black dwarfs yet!)

10. Stars that have more mass than our Sun become SUPERGIANTS instead. As their fuel runs out, the core of a Supergiant will Collapse Violently and the Star will Explode in SUPERNOVA. (An Explosion so Violent that the dying star becomes More Brilliant than an Entire Galaxy.) The Collapsed Core Shrinks to about the Size of a Large City. It is Now a NEUTRON STAR because only neutrons exist in the dense Core.

11. If the Core Continue to Collapse, it Quickly Evolves into a BLACK HOLE **A black hole is So Dense that Nothing can Escape its Gravity Field, Not Even Light**