ASTR 1120 Dark matter halo for galaxies REVIEW General Astronomy: • Dark matter extends Stars & Galaxies beyond visible part of the galaxy -- mass is ~10x stars and gas! � NNOUNCEMENTS • Probably not normal mass that we know of (protons, neutrons, • HOMEWORK #6 DUE TODAY, by 5pm electrons). • HOMEWORK #7 DUE Nov. 10, by 5pm • Most likely subatomic particles, as yet unidentified (weakly interacting massive particles – WIMPs?) REVIEW REVIEW A Case for a Supermassive Black Stars appear to be Hole at the Galactic Center orbiting something massive but • Doppler shift invisible … a measurements black hole! Enclosed mass (M o ) of spiraling stars and gas suggest 3 million M Sun black Orbits of stars hole indicate a mass of about 3-4 million • Still too far out to M sun within 600 Distance from Sgr A* (pc) exclude other Genzel 1996 R Schwarzchild possibilities … We need to be able to see closer in to really prove there is a supermasive black hole!
REVIEW REVIEW State of Affairs at the Galactic Hubble Center Ultra Deep • Stellar orbits have made our Galaxy one of the Field Elliptical Galaxy Elliptical Galaxy best proofs of supermassive black holes at the center of most galaxies. – Millions to billions of times the mass of our Sun. Must be created by something entirely different than a massive star supernova. • Flares are often observed in X-rays and IR – Observations of occasional flares are interpreted as the result of occasional “swallowing” of a gas clump or a star by the giant black hole. Irregular Galaxies Spiral Galaxy Clicker Question Clicker Question Which type of galaxy Which type of galaxy contains a low percentage of contains a low percentage of cool gas and dust? cool gas and dust? A. Spiral A. Spiral B. Elliptical B. Elliptical C. Irregular C. Irregular D. Barred spiral D. Barred spiral E. Everyone but B E. Everyone but B
Hubble classification of galaxy types Where do spirals and ellipticals live? HST: Hickson CG 44 Spirals • Spirals : mostly in groups Ellipticals (3-10 galaxies) Barred spiral The Big Picture: Universe is filled with • Ellipticals - network of galaxies in groups and clusters most often in dense clusters ~100 billion galaxies! of galaxies (involve 100’s to 1000’s) HST: Abell 1689
Clicker Question Pattern of galaxies (3 million+),15 o portion of sky Which of the following is NOT a classification of a type of galaxy? A. Keplerian B. Spiral C. Lenticular D. Elliptical E. Irregular Brighter = more galaxies Clicker Question Our “Local Group” of galaxies Which of the following is NOT a classification of a type of galaxy? A. Keplerian 3 spirals: B. Spiral Andromeda (M31) 3/2 M MW C. Lenticular Milky Way 1 M MW D. Elliptical Triangulum (M33) 1/5 M MW ~21 Galaxies 2 irregulars: E. Irregular LMC 1/8 M MW SMC 1/30 M MW 16+ dwarfs
Triangulum Biggest is Andromeda (Sb - M33) (M33) • Andromeda is ~3 million light years away (or ~30 • 1/5 mass of MW, spiral MW diameters), has classified as Sc ~1.5 mass of MW • Several bright (pink) star forming regions • We see it as it was 3 million years ago, not as it is today! – this is lookback time • Oops! It may crash into MW in about 2 billion years Large & Small Magellanic Clouds LMC has 30 Doradus, home of SN 1987A SMC LMC
Clicker Question Clicker Question What are the What are the Magellanic Clouds? Magellanic Clouds? A. Two nebulae in disk of Milky Way visible only in A. Two nebulae in disk of Milky Way visible only in southern hemisphere southern hemisphere B. Clouds of dust and gas in many places B. Clouds of dust and gas in many places throughout the Milky Way galaxy throughout the Milky Way galaxy C. Two small galaxies in the same group as the C. Two small galaxies in the same group as the Milky Way Milky Way D. Star-forming clouds in constellation Orion D. Star-forming clouds in constellation Orion Mapping the Universe: We How do we get distances to need Distances to Galaxies! things far outside our Galaxy? The problem: or Methods we are familiar with: Radar and Stellar parallax Only useful inside the Solar System A few thousand ly
DISTANCE New Methods: Main-Sequence Fitting ESTIMATE 1 Bootstrap our way • Start with cluster A (upper) whose • Identify (and calibrate) objects that could serve distance known via as “STANDARD CANDLES” -- beyond direct A parallax measurement • Compare with other 1. Make some measure of an object which B cluster B (lower) identifies its luminosity • Get distance to B 2. Use this luminosity and measure apparent from brightness brightness to infer distance to it difference Distances up to ~1 million light years Clicker Question Clicker Question Which cluster is closer? Which cluster is closer? A. Hyades A. Hyades B. Pleiades B. Pleiades A A C. Not enough C. Not enough information to information to B B tell tell
Main Sequence Fitting “pinned DISTANCE Cepheid variable stars ESTIMATE 2 to” nearby Hyades Cluster • “Instability strip” -- region in H-R diagram with large, bright stars • Outer regions of star are Only 151 unstable and tend to ly away pulsate • Star expands and contracts, getting brighter and fainter Reminder (Fig 15.14) DISTANCE Clicker Question Cepheid variable stars ESTIMATE 2 Two Cepheid stars, Fred and Barney, have the same apparent brightness. Fred has a Period - period of 5 days, and Barney of 10 days. Luminosity relation Which is closer ? brighter Cepheids have longer periods A. Fred B. Barney
DISTANCE Tully-Fisher Relation ESTIMATE 3 Why A. Fred ? Period-Luminosity Relation • Fred has a shorter • Fast rotation speeds in period and so must spiral galaxies be less luminous � more mass in galaxy � higher luminosity • Less luminous but the same apparent Measure rotation speeds brightness means to infer luminosity that Fred is closer to us Need bright “edge-on” spirals, estimate tilt Distances up to ~1 billion ly Even brighter: DISTANCE Bright enough to be seen halfway ESTIMATE 4 White dwarf supernovae across observable universe • Nearly the same amount of energy released every time. why? • “Standard explosion” = Useful for mapping the fusion of 1.4 solar universe to the largest masses of distances material
Summary “Distance Ladder” to measure universe Different standard candles are useful for different distances
Recommend
More recommend
