Life Cycle of a Star
Based on Mass of Star
All Stars – Stage 1-Nebula
• Gravity main force, pulls cloud INWARD.
• Temperature = INCREASES
• Gravity based on MASS OF CLOUD.
Orion’s Nebula
All Stars – Stage 1 - PROTOSTAR
• Size DECREASES
• Mass becomes more DENSE
• Temperature hot enough to give off light.
Protostar
All Stars – Stage 2 – Main Sequence
•
•
•
•
Nuclear Fusion begins in core.
Heat pushes OUTWARD
Star becomes STABLE
Now a MAIN SEQUENCE STAR
Main Sequence star
Our Sun
Nuclear Fusion
• Hydrogen fuses into Helium in the Core.
• 4 H  1 He Creates great heat! E = mc2
Red Giant
Medium Mass Star (Sun)-Stage 3
• Red Giant
–
–
–
–
–
Runs out of hydrogen fuel
Fusion occurs in outer shell causing expansion
Outward pressure GREATER than inward pressure.
Sun will expand out to Mars.
Cools and turns Red.
Medium Mass Star – Final Stage
• White Dwarf = Hot but Dim
– Red Giant core collapses
• Inward pressure GREATER than outward pressure
• Outer shell escapes into space = Planetary Nebula
White Dwarf with Planetary Nebula
Foofing 
High Mass Star Stages
• First stages the same but more MASSIVE!
– Nebula
– Protostar
– Main sequence
H-R Diagram
• Where would
High-Mass main
sequence stars
be?
High Mass Star Stages
• Super Giant
– Higher heat and mass allows fusion of heavier elements.
• H  He  C  O Fe
– Outward pressure GREATER than inward pressure
– Expands, runs out of fuel and cools = turns Red
Super Giant
High Mass Star – The End
• Super Giant runs out of fuel = Core collapses
– Inward pressure GREATER than outward pressure
• Core collapse triggers EXPLOSION!
– Explosion = SUPER NOVA
Super Nova
High Mass Star – The End
• Core continues to collapse
– Gravitational force HUGE!
– Turns into a NEUTRON STAR
• Gives off pulsing radio waves (called Pulsar)
High Mass Star – The End
• Black Hole
– If massive enough:
• Continues to collapse into a Black Hole
• Inward pressure GREATER than outward pressure
– Gravity so great, light cannot travel fast enough to escape them.
– Detected by X-rays emitted by things being pulled in.
Black Hole
Life Expectancy of a Star
 The Mass of a star determines the length of
it’s life.
 More Mass = Higher energy used = shorter life.
• Low Mass Star
– 100 Billion years
• Medium Mass Star (our Sun)
– 10 Billion years
• High Mass Star
– 10 Million years
Solar Nebula Theory
A. Nebula
B. Main sequence – accretion disk
formed
C. Collision of particles formed clumps
D. Clumps formed asteroids
E. Asteroids became planets
https://www.youtube.com/watch?v=PL3YNQK
960Y
(3:05 min)
• https://www.youtube.com/watch?v=V
W9FJb1HkDU (2:04 min)