1st Step: Stars form from nebulas Regions of concentrated dust and gas

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??? • 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 Black Holes Info Sheet

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 https://www.youtube.com/watch?v=PM9CQDlQI0A

17. Death of the Sun • But don’t worry! • That’s not going to happen for another 5 billion years • So get out and enjoy the sun!