1. 27.2 Stellar Evolution The Life Cycle of a Star Fox fur nebula Nebula – dark cloud of gas and dust. ~ 70% Hydrogen ~ 28 % Helium ~ 2 % heavier elements We look at stars in every stage of development Stephen Hawking on Gravity https://www.youtube.com/watch?v=R_u2kD4qlrc

2. Dying Star located about 6,500 light-years away in the constellation Hercules Lagoon Nebula’s star “Nursery”. Taken by European space telescope http://www.space.com/12605-50-deep-space-nebula-photos.html Descriptions of Nebulae:

3. Plasma cloud in Orion Nebula Blue is X-ray emission Red Cosmic Square (Near perfect symmetry)

4.  Orion nebula  Cat’s eye nebula Horse head nebulaCarina NebulaEagle Nebula http://hubblesite.org/gallery/tours/tour-carina/Carina nebulae

5. Butterfly nebula Cone nebula Eskimo nebula Three-ring Nebula Crab Nebula Helix Nebula

6. 1.Nebula shrinks 2.Collisions release energy 3.Matter builds up w/in the cloud 4.As nebula shrinks, it spins more rapidly 5.Matter increases at the center 6.Pressure & Temperature rise 7.At 10 million degrees °C, a Protostar is formed Birth of a Star The energy from fusion balances the force of gravity, maintaining a stable size.

7. Life Cycle of a Star Small protostar (low mass)  main-sequence  giant  nova  white dwarf We expect our sun to become a white dwarf. Large protostar  main-sequence  supergiant  supernova  neutron star or black hole

8. Types of Stars Protostar – new star formed from nebulae gases Main-sequence – longest stage; energy generated by nuclear fusion Giant – old star; nearly all H atoms fused into He; expands rapidly White dwarf – star loses gases (planetary nebulae); gravity collapses matter inward The hot dense cores of white dwarfs can burn for billions of years They may also explode (nova) Small protostar (low mass)  main-sequence  giant  nova  white dwarf

9. Types of Stars Supergiants have a mass 10 – 100 times larger than our sun. Collapse of star occurs at higher pressure & temperature. Nuclear fusion begins again forming carbon and heavier elements. When core is nearly all iron, nuclear fusion stops. When iron core collapses, the star explodes, forming the 92 elements found on earth. In 1054, Chinese astronomers documented an explosion in the sky that was so bright they could see it during the day for 3 weeks. Large protostar  main-sequence  supergiant  supernova  neutron star or black hole Crab NEBULA https://www.youtube.com/watch?v=0GD8-Lj0tFI Neutron star – core left from a supernova Pulsar – a fast spinning neutron star; emits radio waves or other ER Black hole – denser than neutron stars, not even light escapes Blue star life cycle https://www.youtube.com/watch?v=fKWAM_ubF1k

10. Looking ahead Blue Supergiant Star Explosion (Fermi observations) https://www.youtube.com/watch?v=3vKtQFpi_ns https://www.youtube.com/watch?v=pS4MYtNVeC0

11. 27.3 Star Groups Constellation – seemingly fixed patterns of stars. We use constellations to find specific stars and other space phenomenon. 88 recognized constellations. 100,000 BC 100,000 years from now Now

12. Galaxies – large groups of stars, bound together by gravity. Contains billions of stars, gas, dust, and nebulae. Galaxies The Hubble Deep Field telescope reveals thousands of galaxies in a single picture. We estimate there are 100-200 billion galaxies, and classify by shape.

14. Types of Galaxies 1.Spiral galaxy – 3 main components... Bulge – spherical, in the center; older stars Disk – dust, gas, and younger stars; “arm” Halo – loose, spherical structure around bulge; contains old clusters of stars Barred spiral galaxies have a bar of stars across the center 

15. Types of Galaxies 2.Elliptical galaxy – Spherical to disk shape; No young stars and little dust or gas; No particular axis of rotation

16. Types of Galaxies 3.Irregular galaxy – no particular shape; stars unevenly distributed; many hot young stars. A lot of dust, blocking light from stars

17. The Milky Way – Our own Galaxy Barred spiral galaxy ~ 100,000 ly across 4 large spiral arms (2 major) Our sun is in the Orion arm Our solar system travels about 515,000 mph It takes ~ 230 million years to go around one time Galaxy contains star clusters, groups of hundreds of stars. Multiple-star systems more common than single.

18. Formation of the Universe Evidence of the Big Bang Theory Edwin Hubble’s 1929 discovery of the expanding universe Background radiation & Doppler effect (Red shift) Doppler effect – Red shift https://www.youtube.com/watch?v=Kg9F5pN5tlI Grad student gives news https://www.youtube.com/watch?v=ZlfIVEy_YOA ESO Accelerating expanding Universe https://www.youtube.com/watch?v=lUkwWqF0nGM Hubble and red shift https://www.youtube.com/watch?v=hVApTLE7Csc Note: For theories in science, we require multiple lines of evidence... Evidence from different fields

19. Formation of the Universe Evidence of the Big Bang Theory Einstein’s general theory of relativity Dark energy Einstein’s Relativity: https://www.youtube.com/watch?annotation_id=annotation_607616&feature=iv&src_vid=30KfPtHec4s&v=G-R8LGy-OVs Dark energy https://www.youtube.com/watch?v=P8wRDGEl4F8 Part 1: https://www.youtube.com/watch?v=30KfPtHec4shttps://www.youtube.com/watch?v=30KfPtHec4s Dark energy Don’t assume... Professors have student measure how much galaxies are slowing down. https://www.youtube.com/watch?v=P8wRDGEl4F8 Inflation theory (like blowing up a balloon) http://space.io9.com/translating-physicist-to-human-1546963824