Lives of Stars Section 3

1. Lives of StarsSection 3

2. Nebula • Large cloud of gas and dust spread out in an immense volume • All stars are born in a nebula, large cloud of gas and dust.

3. Protostar • Gas and dust begin to collect due to gravity. • Once enough material has formed together, a protostar is created. • This is the beginnings of what will become a star. A star is born when nuclear fusion begins.

4. Lifetimes of Stars • Like automobiles burning through their gas, the length a star lives depends on its mass. • Larger, more massive stars live shorter while less massive stars live longer.

5. Deaths of Stars • As the star runs out of fuel, its core shrinks and gets hotter. • As it does so, it heats the gases surrounding it which causes the outer layers to expand. • The star will then become a black dwarf or black hole dependent upon its starting mass.

6. Less Massive Stars NebulaProtostar Low-mass or medium-mass star Red GiantPlanetary Nebula White Dwarf Black Dwarf

8. Medium Sized Stars • Medium sized stars are the most common in the universe. An example is our sun. Medium size stars are 10 times more massive than a red dwarf

9. Red Giant • 10-100 times the size of our sun. It shines red and it is about 3000oC.

10. Planetary Nebula • After the red giant, the star will create a planetary nebula, which is the glowing gas of the outer layers as they expand away from the core.

11. White Dwarf • The only thing that remains after is the core of the star, a very hot dense, white dwarf. After billions of years this will eventually cool to become a black dwarf.

13. Greater Mass Stars • NebulaProtostar High-mass star Supergiant Supernova Neutron Star Black Hole

16. Red Supergiant • High mass stars quickly evolve into brilliant supergiants.

17. Supernova • All massive stars will explode in a supernova.

18. Supernova Images

19. Neutron Stars • The lower mass high mass stars will instead become neutron stars. • Neutron stars spin rapidly and emit radio waves.

20. Black Holes • However, only the most massive will become black holes. • Remains of a supernova which contains enough gravity that light cannot escape • After a very massive star dies in a supernova explosion, more than 5 times the mass of the sun may be left • The gravity of this mass is so strong that the gas is pulled inward, packing the gas into smaller and smaller space.

21. Black Holes • Not able to detect a black hole directly because no light, no radio waves, or any other form of radiation can ever get out of a black hole • Detect black hole indirectly • Gas near a black hole is pulled so strongly that it revolves faster and faster around the black hole • Friction heats the gas up • Astronomers can detect X-rays coming from the hot gas and infer that a black hole is present

23. Reminders • Only stars with more than 40 times the mass of the sun form black holes when they die • Other high mass stars become neutron stars when they die • When a star begins to run out of hydrogen, it can become a red giant or supergiant • United Streaming Video • Brain Pop Segment