1. Life Cycle of Stars 1st Step: Stars form from nebulas
Regions of concentrated dust and gas
Gas and dust begin to collide, contract and heat up
All due to gravity

2. Life Cycle of Stars 2nd Step:
As nebula contracts, a small star is formed
Called a protostar
Eventually, the protostar will begin nuclear fusion
Hydrogen protons attract to each other
Strong nuclear force
Fusion begins
Necessary for stars to survive

3. Life Cycle of Stars 3rd Step: Star joins the main sequence
90% of stars spend life here
Nuclear fusion = Hydrogen into Helium
It’s basically a balancing act:
Nuclear fusion provides energy that moves outward from the core
Gravity pulls everything inward
So the outward force of fusion equals the inward force of gravity and the star stays relatively stable

4. Life Cycle of Stars
Danish astronomer Ejnar Hertzsprung and America Henry Russel studied the light emitted by a great number of stars and game up with graph – The Hertzsprung-Russell Diagram

5. Life Cycle of Stars
They found that 90% of all stars lie along a fairly straight line (the main sequence)
Basically, the brighter they are, the hotter they are
The coolest stars burn a red colour while the hottest are blue
Mass of star determines location on main sequence
But there are a number of stars that burn brighter but cooler (red giants)
Another group burn hotter but not as bright (white dwarfs)

6. Life Cycle of Stars Beginning of the End:
Stars begin to die when they run out of hydrogen
Gravity begins to take over
Star begins to shrink; outer core of hydrogen begins to fuse
Star gets bigger

7. Life Cycle of Stars Beginning of the End:
When a star gets bigger, it cools down
Red giant
Eventually, star can fuse helium into other elements
Carbon, oxygen, and other heavier elements

8. Life Cycle of Stars Beginning of the End:
Once star runs out of “fuel”, star shrinks under its own gravity
Turn into a white dwarf, neutron star, or black hole

9. Life Cycle of Stars Death of Stars:
What stars end up as depends on mass
Low and Medium mass stars
Planetary nebula white dwarf
High mass stars
Supernova neutron star or black hole

10. Life Cycle of Stars
Death of Stars: Low and Medium Mass (like our Sun!!)
Main Sequence Star
Red Giant
Planetary Nebula
White Dwarf

11. Life Cycle of Stars Death of Stars: High Mass Main Sequence Star
Red Super Giant
Supernova
Neutron Star
Black Hole

12. Black Holes What is a Black Hole??? Black Holes Info Sheet
An object so massive and dense that not even light can escape its gravity
The end result from a supernova of a star that has a mass greater than 3x the sun

13. Life Cycle of Stars High Mass Stars: Mass greater than 8x our sun
Create high mass elements such as iron
Neutron Star
Formed if remaining star < 3x sun’s mass
Black Holes
Formed if remaining star > 3x sun’s mass

14. Life Cycle of the Sun
As fusion begins to slow down, the core of the sun will contract
Temperature in the core will rise
The outer layers of the sun will expand, consuming in the inner planets
Sun will become a Red Giant

15. Life Cycle of the Sun

16. Life Cycle of the Sun
Core of the sun will begin to fuse helium into larger elements such as carbon and oxygen
Continuing over the next 100 million years…
Core will become entirely carbon and oxygen
Core will contract
Outer layers will expand
Outer layers will form a planetary nebula
Core of sun will become a white dwarf
Youtube video Life Cycle of Stars

17. Death of the Sun But don’t worry!
That’s not going to happen for another billion years
So get out and enjoy the sun!