STARS

1. STARS Amole Spectra of Science 2013

2. What are Stars? • A large celestial body of hot gas that emits light • Greeks grouped stars in patterns called constellations • Use the unit light-year to measure distances between stars • 9.5 x 1015 m • Driven by nuclear fusion reactions

3. Why do Stars look Different from One Another? • Size • Distance from Earth • Temperature • Stage of Life Cycle

4. Characteristics of Stars • Color indicates temperature • Blue (Short λ) = Hot • Red (Long λ) = Cool • The hotter they are the faster they burn out • Magnitude • Brightness • Smaller numbers represent brightest stars

5. Classification of Stars • Classified by temperature and brightness • Decreasing Temperature and brightness •                 • Oh, Be AFine Girl, Kiss Me

6. Classification of Stars

7. H-R Diagram

8. Nuclear Fusion • Strong gravitational forces hold stars together • Energy from fusion creates outward pressure balancing inward pull • Hydrogen atoms are fused to form helium

9. Layers of Stars • Energy moves through layers by radiation and convection • May take millions of years for energy to work its way through star to surface • After leaving the surface it enters space traveling at the speed of light, • 3 x 108 m/s

10. Temperatures of the Sun

11. What Happens When a Star Runs out of H? • Begins to fuse He • Then, a succession of heavier elements • Iron is the most stable; it requires energy verses creating it • Star begins to die

12. Life Cycle of Stars

13. Stellar Nebula • Nebulas are clouds of dust and gas from which stars are born • Grains of carbon and silicon • Matter compresses due to own gravity • Temperature and pressure slowly increase from compaction Omega Nebula

14. Eagle Nebula

15. Lagoon Nebula

16. Bubble Nebula

17. Crescent Nebula

18. Orion Nebula

19. Crab Nebula

20. Adult Star • Actively undergoing hydrogen fusion • Main Sequence star • Spends most of its lifetime in this phase • 90% of stars in the galaxy are in this phase • An average size like our sun will “burn” much longer than a larger, more massive star

21. Red Giants and Supergiants • When a star runs out of hydrogen, it begins to die • Energy from fusion no longer counteracts gravity, and the core collapses • Causes outer layers to expand • Average stars create Red Giants • Massive stars create Red Supergiants

22. White and Black Dwarfs • Core runs out of He, and is no longer able to fuse the remaining heavier elements • The star blows its outer layer away • The core remains behind and burns as a white dwarf • Eventually it cools to become a black dwarf Little Ghost Nebula

23. Stingray Nebula

24. Ring Nebula

25. Supernova • Massive stars end in violent explosions that blow away the outer layers of the star • These stars result in either a neutron star or supernova

26. Neutron Star • Leftover core has between 1.4 – 3 solar masses • Collapses so much that protons and electrons combine to form neutrons • Very dense (a thimbleful weights more than 100 million tons) • Emit radio waves (pulsars)

27. Black hole • Leftover core has a mass greater than 3 solar masses • Collapses so much that not even light can escape its gravity

28. Milky Way Black Hole

29. Death of a Star Simulations

30. Life Cycle of Stars