Doubly Dead Stars

1. Doubly Dead Stars • A binary system eventually ends as two compact objects • Usually nothing else happens • If very close (neutron stars or black holes) more happens • Stars emit gravitational waves – they move closer • Merge to make black hole • Some gamma ray bursters occur this way Three ways to make a black hole • Very massive star death (> 30 MSun) • Accretion onto neutron star • Merger of two neutron stars

2. Gravitational Waves • When two neutron stars, two black holes, or one of each merge, they should cause fluctuations in space–time • Gravitational waves • February 11, 2016: LIGO announces discovery of gravitational waves • Produced by merging black holes • 29 MSun merged with 37 Msun • 1.3 billion light years away • August 17, 2017: LIGO announces detection of gravitational waves from neutron star merger • Combined with gamma ray burst • Followed by supernova observation

3. Cosmic Recycling • It is believed that the hydrogen and helium in stars was created at the beginning of time, the “big bang” • What about the other elements? • Red Giants and Double Shell-burning stars lose gas from their outer layers • Add carbon, oxygen and nitrogen to the universe • Supernovae contribute all other elements • Both Massive Star Supernovae and White Dwarf Supernovae • We now think neutron star mergers also produce some of the heaviest elements • Such as gold • Later generations of stellar systems contain all elements • Like our stellar system!

4. End of Material for Test 3 L = 4d2B Test 3 Review Online 4 H + 2e - He + 2 neutrino + energy Questions?

5. The Milky Way Levels of Organization • From smallest to biggest: • Stellar systems (binaries, etc.) • Stellar Clusters • Galaxies • Galaxy Groups and Clusters • Galaxy Superclusters • The Universe Our Galaxy is called the Milky Way

6. The Milky Way: Visible Light Center of Galaxy • Obscured by gas and dust Galactic Plane

7. The Milky Way The central portion Baade’s Window

8. The Milky Way – From Outside

9. The Milky Way – From Outside

10. The Milky Way – Edge On Q. 87: Pictures of Milky Way from the Outside

11. The Milky Way – Artist’s Conception • Our galaxy is hard to study because we are inside it • We are in the galactic plane, filled with obscuring dust • Other galaxies are hardto study because theyare far away • Generalize from far away to nearby and vice versa Youare here

12. The Milky Way – Basic Structure • Galaxies and larger structures are incrediblylarge compared to anything we havestudied up to now • We need newunits to describe it • The disk • The bulge • The nucleus • The halo • Globular clusters The Sun Distances ly = 0.931016 m kly = 103 ly Mly = 106 ly Gly = 109 ly

13. The Disk – Dimensions and Structure • The disk • The bulge • The nucleus • The halo • Globular clusters • A large, flat disk, shaped like a pancake • About 100 kly in diameter • About 3 kly thick • We are about half way out • Has prominent spiral structure 27 kly The Sun 3 kly 100 kly

14. The Disk - Composition • Stars, mixture of young and old • Circular orbits in plane of galaxy • From 0 to about 10 Gyr • Open clusters • The interstellar medium • Hot bubbles • Atomic hydrogen clouds • Molecular clouds • Ionization nebulae • Dust • Obscures and reddens things • Causes “reflection nebulae” • The disk • The bulge • The nucleus • The halo • Globular clusters

15. Open Clusters NGC 290 M35 NGC 2158 Pleiades M6 M36

16. Hot Bubbles • The disk • The bulge • The nucleus • The halo • Globular clusters • Gas heated by supernovae and other violent events • Gas is very thin • Gas is very hot and ionized • Temperatures up to 106 K • Can be tracedout by X-rays

17. Hot Bubbles - Images

18. Atomic Hydrogen Clouds Slightly cooler regions of gas • Hydrogen atoms produce 21 cm line • Electron and proton are spinning and have magnetic interactions • When electron spin flips over, 21 cm radio emission is seen • 21 cm line used to map out our disk • Can also get accurate Doppler shift • The disk • The bulge • The nucleus • The halo • Globular clusters Radio waves Q. 88: Doppler Shift From 21 cm Line

19. The 21 cm line

20. Approximate Map of Galaxy

21. Molecular Clouds Coldest and densest regions • Atoms join together to make molecules • Principally hydrogen (H2), but this is difficult to detect • Other molecules vibrate to produce characteristic radio waves • These regions are where new stars can form Carbon monoxide (CO) emissions from cool clouds in our galaxy

22. Molecular Clouds – Eagle Nebula

23. Molecular Clouds

24. Molecular Clouds – Keyhole and Orion

25. Molecular Clouds

26. Molecular Clouds – Horsehead Nebula

27. Ionization (Emission) Nebulae • The disk • The bulge • The nucleus • The halo • Globular clusters • Light from hot stars ionizes hydrogen • Hot thin gas • When it recombines, light is made Q. 89: Spectrum from an Emission Nebula Light

28. Ionization (Emission) Nebulae

29. Ionization (Emission) Nebulae

30. Labeled Eagle Nebula