1. Life Cycle of a Star

2. Star Formation
Formed when a huge interstellar gas cloud (typically hydrogen) condenses due to gravity.
As the cloud gets smaller, heat is generated and particles move more. This allows for fusion of hydrogen atoms.

3. Hydrogen Fusion (birth of a star)
2 Hydrogen atoms collide hard enough to form 1 larger Helium atom
A tiny bit of matter seems to disappear but actually it is converted into energy (E = mc2).
This energy is released as heat and light.

4. Star Death When Hydrogen fuel (atoms) run out, Helium fusion begins.
When Helium runs out, the outer layers cool and the star swells (red-giant phase)
Next phase depends on the mass of the star

5. Star Death 1. Mass of Sun or less (most stars)
Outer layers eject leaving just the core
Core contracts and becomes very dense (white dwarf)
This gradually cools and fades away.

6. Star Death 2. More massive than the Sun
Core contracts and begins fusing heavier elements up to iron.
Eventually fusion stops and core collapses
Explosive ejection of outer layers (Supernova explosion)
Dense core left (neutron star)
Neutron star may become a black hole if massive enough
More massive stars lead the shortest lives!! They burn their fuel quickly!

7. Leftovers Stars recycle their matter as it is released in space.
It is used to form new stars, planets, & even us!
We are made of star dust!

9. Hertzsprung-Russell Diagram
Scatter graph of stars showing the relationship between Absolute Magnitude (brightness) and temperature
Stars are classified according to their color, size, mass, luminosity, temperature
Most stars lie on the Main Sequence band
Star’s mass determines the star’s place on the Main Sequence