Tour of Galaxies. Sgr A* VLT in IR + adaptive optics. orbits. ASTR 1040 Accel Astro: Stars & Galaxies VLT IR+AO

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1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Kyle Augustson Lecture 23 Tues 8 Apr 08 zeus.colorado.edu/astr1040-toomre toomre Tour of Galaxies Briefly revisit Monster in the Milky Way (supermassive black hole at the center) Hubble using Cepheids showed Andromeda is a distinct island universe another Galaxy! Today turn to Galaxies (Chap 20) starting with Hubble s s scheme to classify spiral galaxies, ellipticals,, and irregulars Look at our local group of galaxies (Milky Way, Andromeda, Triangulum,, LMC, SMC + dwarfs) Re-read 20.1 Galaxy Types, and for Thurs lecture 20.2 Measuring Cosmic Distances and 20.3 Hubble s s Law New Homework Set 10 passed out Planetarium listed for 10 Apr replaced by lecture REVISIT Black Hole at MW center Sgr A* Radio mapping of galactic center 240 ly VLT IR+AO Sgr A* orbits VLT in IR + adaptive optics Star motion around black hole at galactic center VLT: IR+AO 1

2 Rotation velocity at galaxy center Sgr A* orbits Some of central mass is stars, joined by 3.7 +/- 0.2 million solar mass BLACK HOLE But further 20% uncertainty from distance determination Black hole still less than 1/1000 of MW mass Question: Why no powerful jet and accretion disk near MW s supermassive black hole? Why not much emission in X-rays?.though other signs of activity Answer: maybe it has eaten all it can at least for now? Large-scale structure in Milky Way We can observe the atomic hydrogen in interstellar gas in Milky Way with. A. space-based ultraviolet telescopes D. B. x-ray telescopes C. ground-based visible light telescopes D. 21 cm observations by radio telescopes Measuring galactic distances Edwin Hubble made breakthrough using Cepheid variables to measure distance Found Andromeda far outside Milky Way HOW DID IT ALL BEGIN? Cepheid variable stars as distance indicators: standard candle Vital discovery by Henrietta Leavitt (1912) Huge step forward in thinking about universe NGC

3 Cepheid stars in H-R H R diagram Instability strip -- region in H-R H R diagram with large, bright stars Outer regions of star are unstable and tend to pulsate Star expands and contracts, getting brighter and fainter Reminder (Fig 15.14) Period - Luminosity relation Cepheid variable stars brighter Cepheids have longer periods Andromeda found to be far outside Milky Way another island universe : galaxy! Edwin Hubble in 1924 identified Cepheids in Andromeda (M33) showed they were far outside of Milky Way! Now known distance: 2.3 million ly His first big discovery (more to come) Hubble using new 100 Hooker telescope at Mt. Wilson (above LA) 100 Hooker telescope at Mt Wilson Begins new era in 1924! Andromeda M31 (Sb( Sb) Andromeda surprises with Spitzer in IR NGC205 NGC205 M32 First galaxy shown by Hubble (1924) to be a distinct island universe M31 M million ly away 260,000 ly in diameter 3.6 microns (blue), 4.5 (green) 8 microns (red) 3

4 M31: 11,000 image composite with Spitzer M31: Forensic evidence of galactic collision M32 plunged through disk on polar axis ~210 My ago?? 1 Striking rings of dust and starbirth 2 Ring splits into two, forming hole on lower right 3 Delicate tracings of spiral arms into very center M31: Beautiful neighbor in UV and IR Hubble s scheme to label galaxies spirals S ellipticals E lenticular GALEX: SPITZER: Far-UV (blue) young hot massive stars Near-UV (green) relatively older stars 24 micron IR (red) cool, dusty star forming + some irregulars barred spirals SB Tuning fork shown with mugshots of galaxies spirals ellipticals spirals-barred M101 4

5 Spirals ~80% of galaxies Disks (with spiral arms) + Spheroids (bulges+halos) NGC 4414 Barred spiral galaxies Spiral arms emerge from central bar M100 center NGC 1365 NGC 1300 HST: Center of barred spiral NGC 1365 Lenticulars (lens-shaped) shaped) Disks, but less gas and star formation Note lack of dust & pink nebulae IR view Ellipticals ~15% of galaxies Round or slightly flattened Very little cold gas, dust, or young stars Dwarf ellipticals Most common type of galaxy? Only know nearby ones (since faint!) Reddish color = old stars (red giants, red main sequence) NGC 205 2MASS 5

6 Irregulars Galaxies in transformation? Often LOTS of star birth M82 Where do spirals and ellipticals live? Spirals mostly in groups (3-10 galaxies) HST: Hickson CG 87 NGC 674 Ellipticals - most often in dense clusters of galaxies (involve 100 s to 1000 s) The Big Picture: Universe is filled with network of galaxies in groups and clusters ~100 billion galaxies! HST: Abell 1689 Pattern of galaxies (3 million+),15 o portion of sky Clicker reading ahead What are the Magellanic Clouds? C. Brighter = more galaxies A. Two nebulae in disk of Milky Way visible only in southern hemisphere B. Clouds of dust and gas in many places throughout the Milky Way galaxy C. Two small galaxies that orbit Milky Way D. Star-forming clouds in constellation Orion 6

7 Our local group of galaxies 3 spirals: Andromeda (M31) Milky Way Triangulum (M33) 2 irregulars: LMC SMC 16+ dwarfs Biggest is Andromeda (Sb - M31) Andromeda is ~3 million light years away (or ~30 MW diameters), has ~1.5 mass of MW We see her as she was 3 million years ago, not as she is today! this is lookback time Oops! she may crash into MW in about 2 billion years Triangulum (M33) 1/5 mass of MW, spiral classified as Sc Several bright (pink) star forming regions Large & Small Magellanic Clouds SMC LMC LMC has 30 Doradus,, home of SN 1987A SN 1987a before and after 7