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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.
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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 = 4d2B Test 3 Review Online 4 H + 2e - He + 2 neutrino + energy Questions?
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 – 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 hardto study because theyare far away • Generalize from far away to nearby and vice versa Youare here
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 = 0.931016 m kly = 103 ly Mly = 106 ly Gly = 109 ly
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
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 • 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
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
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
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