ASTR 1120 REVIEW Andromeda found to be far outside Milky Way! General Astronomy: Stars & Galaxies • Edwin Hubble in 1924 identified Cepheids in Andromeda (M33) � � NNOUNCEMENTS NNOUNCEMENTS showed they were far outside of Milky Way! • Homework #7 due today, by 5pm – “Island Universes” • His first big discovery! • Homework #8 due next Tue, Nov. 17, by 5pm • But then he turned his attention to OTHER • Midterm #3 on Thu, Nov.19 galaxies Hubble using new • EXTRA OBSERVING NIGHT - THU 12th, from 100” Hooker telescope 8:30pm (20 students every 1/2 hr) at Mt. Wilson (above LA) Balloon analogy for REVIEW “Hubble’s Law” expanding universe REVIEW v = H o � d • Each dot on the balloon can be Velocity of Hubble’s Distance Recession Constant thought of as a (Mpc) (Doppler Shift) (km/sec/Mpc) galaxy. (km/sec) velocity As the balloon expands, galaxies move farther away from each other distance
The Hubble Deep Field Chapter 21: Galaxy Evolution • Observing galaxies at different redshifts Some (lookback times) galaxies very � young, • Allows us to assemble a sequence of when the Universe galaxies showing birth and evolution was about � a tenth of its current • Check via computer models of gas, age! gravity and star formation Making of a spiral galaxy REVIEW REVIEW Small variant in spiral making … • Start with a fairly • Several smaller uniform cloud of hydrogen protogalactic clouds may have merged to • Gravitational collapse form a single forms protogalactic large galaxy clouds • May explain • First stars are born in this spheroid (such variations in stars are billions of metallicities in years old � “fossil the halo stars record”)
REVIEW Forming a disk Making ellipticals with spiral 1. Higher density: much faster star formation • As more material uses up all the gas collapses, angular – Nothing left to make a disk momentum spins it or into a disk 2. Lower spin – Gas used up before angular momentum took • Stars now formed over in dense spiral • Now we see a sphere arms – disk stars of old stars are younger! Angular momentum of protogalactic cloud important in spiral galaxy formation Clicker Question Or perhaps a different scenario…. • Spiral galaxy collisions Why are collisions between destroy disks, leave galaxies more likely than behind elliptical between stars within a galaxy? • Burst of star formation uses up all the gas A. Galaxies are much larger than stars • Leftovers: train wreck B. Galaxies travel through space much faster than stars • Ellipticals more common in dense galaxy clusters C. Relative to their sizes, galaxies are closer (centers of clusters together than stars contain central dominant galaxies) D. Galaxies have higher redshifts than stars NGC 4038/39 Antennae
Clicker Question Why are collisions between galaxies more likely than between stars within a galaxy? A. Galaxies are much larger than stars B. Galaxies travel through space much faster than stars C. Relative to their sizes, galaxies are closer together than stars D. Galaxies have higher redshifts than stars Colliding galaxies – “The Antennae” Colliding Galaxies: NGC 4676 HST detail: NGC 4038/39 “Mice” with HST Advanced Camera for Surveys
Stephan’s Quintet in HST detail Many interacting galaxy systems A mature example: It may happen to us in future! Elliptical shape but with dust lanes? Andromeda (M31) in future
Starburst Galaxies Messages From Galaxy Interactions 1. In dense clusters, galaxy collisions (grazing or even head-on) must have been common 2. With successive passages, spiral galaxies can tumble together to form a big elliptical 3. Vastly increased star birth from shocking the gas and dust (starburst galaxies; coming up next!) M82 - visible Chandra – X-ray 4. Start rapid feeding of supermassive black • Milky Way forms about 1 new star per year hole lurking at center of most galaxies • Starburst galaxies form 100’s of stars per year (quasars; coming up soon!) Vigorous star birth – “The Antennae” Starburst galaxies emit most of their light at infrared wavelengths • Star formation heats dust to very hot temperatures – Hot dust glows strongly in the infrared • Much evidence for giant supernova-driven galactic winds • Usually triggered by galaxy collisions or close passages HST detail: NGC 4038/39 of another galaxy
Active Galactic Nuclei: Starburst Another Type of Galactic Fireworks galaxy in fine detail • Galaxies with strange stuff going on in their centers NGC 3310 - HST • Some galaxies at high redshift (large lookback times) have extremely active centers Big open two-sided – More than 1000 times the light of the entire Milky spiral structure Way combined from a point source at the center!! --> tidal interaction Quasars Clicker Question What is the most likely source of the • Quasi-Stellar Radio Source light from bright nuclei (radio, visible, X-rays) in active galaxies? • Nuclei so bright (at nearly all wavelengths) that the rest of the A. Thermal radiation from a massive star galaxy is not easily cluster seen B. Emission lines from hot gas C. 21 cm from hydrogen gas • First discovered as radio sources - then D. H-alpha from hydrogen gas found to have very E. Synchrotron radiation from a black hole high redshifts!
Clicker Question E. Synchrotron What is the most likely source of the light from bright nuclei (radio, visible, • Only synchrotron X-rays) in active galaxies? radiation is bright at both radio and A. Thermal radiation from a massive star X-ray wavelengths cluster (far ends of the B. Emission lines from hot gas spectrum) C. 21 cm from hydrogen gas D. H-alpha from hydrogen gas E. Synchrotron radiation from a black hole Whatever is powering these Quasar Central Engines QSO’s must be very small!! How do quasars emit so much light in so little space? • Some quasars can double their brightness within a few hours. • They are powered by accretion disks around JET supermassive black • Therefore they cannot be larger than a few light- holes hours across (solar system size) – Why? Think about the time it takes light from the front • In some quasars, huge DISK jets of material are shot of the object to get to us compared to the light from the out at the poles. These back. jets are strong radio sources.
“Central Engine” -- artist’s conception Prototypical “radio galaxy” • Accretion disk around super- massive black hole Giant elliptical galaxy NGC 5128 • Disk itself may or with dust lane may not be obscured (from spiral galaxy?) by dust + Centaurus A • If bright nucleus is radio source visible, looks like a (color lobes) quasar, if not, then its a radio galaxy Cygnus A radio jets Radio tails: many shapes NGC 1265 – 100K ly 400,000 ly Jet as fine thread, big lobes at end, central hot spot VLA 3C 31 – 2 M light years
M87 – elliptical with jet Another example of “central beaming engine” 800 km/s 60 ly away • Active galactic nucleus beams out radio active nucleus - HST very narrow jet • Accretion disk shows gas orbiting a 2.7 billion solar mass black hole – • 400 light year wide disk of material in core of elliptical galaxy with radio first real proof in an active nucleus! jets – looks like a supermassive black hole at work! Disk around ‘black hole’ in NGC 7052 Do ALL galaxies have supermassive black holes in their centers? • likely YES! • Linked to the process of galaxy formation • More quasars seen in the distant (early) GROUND universe than now • Black holes gradually grow, but can run out of available fuel and become nearly invisible (like in our Milky Way) HST
Somehow, the rest of the galaxy knows about the SMBH during formation!!
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