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

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

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!

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

Levels of Organization 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

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

The Milky Way The central portion Baade’s Window

The Milky Way – From Outside

The Milky Way – From Outside

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

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 hard to study because they are far away Generalize from far away to nearby and vice versa You are here

The Milky Way – Basic Structure Galaxies and larger structures are incredibly large compared to anything we have studied up to now We need new units to describe it The Sun The disk The bulge The nucleus The halo Globular clusters Distances ly = 0.931016 m kly = 103 ly Mly = 106 ly Gly = 109 ly

The Disk – Dimensions and Structure 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

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

Open Clusters NGC 290 M35 NGC 2158 Pleiades M6 M36

Hot Bubbles The disk Gas heated by supernovae and other violent events 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 traced out by X-rays

Hot Bubbles - Images

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

The 21 cm line

Approximate Map of Galaxy

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

Molecular Clouds – Eagle Nebula

Molecular Clouds

Molecular Clouds – Keyhole and Orion

Molecular Clouds

Molecular Clouds – Horsehead Nebula

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

Ionization (Emission) Nebulae

Ionization (Emission) Nebulae

Labeled Eagle Nebula