Tour of Galaxies. stuff: dust SEMI-WARM. ASTR 1040 Accel Astro: Stars & Galaxies. Dust+dark molecular clouds. in close-up VLT.

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1 ASTR 1040 Accel Astro: Stars & Galaxies Prof. Juri Toomre TA: Nicholas Nelson, Zeeshan Parkar Lecture 23 Tues 6 Apr 2010 zeus.colorado.edu/astr1040-toomre toomre Tour of Galaxies Role of dust in absorbing/scattering light How can we map the spiral arm structure of our Milky Way galaxy? Next turn to mysterious galactic center in Milky Way: supermassive black hole Hubble using Cepheids showed Andromeda is a distinct island universe another Galaxy! 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 ISM: A little DUST goes a long way! Reddens the light Absorbs the light SEMI-WARM stuff: dust DUST: absorbs visible and UV light Transparent to long wavelengths (red, IR, radio) Emits IR light Horsehead Nebula Dust+dark molecular clouds Horsehead in close-up VLT Eagle Nebula 1

2 Clouds + dust in Eagle Nebula Rosetta Nebula O & B star carving + dust filaments Dark and dusty stellar nurseries Widefield Infrared Survey Explorer (WISE) NGC 3603 Nebula RCW 49 Stellar jewels Spitzer IR Complex cycle is ongoing. WHERE are we in MW? Dust makes it hard to estimate distances (stars dimmed) Globular clusters on COBE IR sky image Disk is busy! Cycle The of Star-Gas- Star stars Cycle gas stars SUN X Shapley s (1920) distances to globular clusters: Sun at 18 kpc from center (twice too far!) 2

3 Clicker galaxy center We want to map out the structure of the central core of the Milky Way. What wavelength should we be using, and why? A. IR or radio B. visible light C. X-rays A. COLD stuff: dark clouds Molecular CLOUDS Dark, dusty, cold (10-30 K) K Emit molecular emission lines in far IR, radio Orion image here in carbon monoxide (CO) -- colors are Doppler shifts CO Doppler Images COLD hydrogen throughout Even the coldest hydrogen emits faint emission line in the RADIO Wavelength 21 cm Q: Just HOW do we know that MW has spiral structure? A: Radio astronomers could map it with 21-cm line of hydrogen Emission from flip of electron from spinup to spindown state All sky 21 cm radio mapping Green Bank 100 m Radio Telescope VA 21 cm emission (radio) Sampling neutral hydrogen atoms (cold) also how MRI does it in medical imaging! 3

4 VLBA Radio Telescope Owens Valley Very Large Array (VLA) Socorro NM VLA - Sicorro Radio mapping cool H clouds in MW disk SUN o Another view of 21 cm radio mapping SUN Beam cuts across different spiral arms o o Doppler shifted radio emission Radio map (21 cm) of spiral structure in MW Ragged spiral structure revealed SUN x Close-up view of our vicinity Emitted radio waves can penetrate through gas and dust o GALAXY CENTER o Orion arm toward galactic center 4

5 Center of our galaxy Dust obscures our vision of much of the galaxy in visible and UV light. MW center 39 box X-rays only highlight the hottest and weirdest places Located in direction of Sagittarius IR and radio light pass through unaffected, show dust, stars, gas Galactic center: IR reveals a dense star cluster Unusual activity at galaxy center IR 1 Radio mapping of galactic center Radio 3 IR 5 Radio 4 Zooming in on Sagittarius A* Radio 2 5

6 Sgr A* orbits VLT in IR + adaptive optics Sgr A* VLT IR+AO Star motion around black hole at galactic center Sgr A* orbits VLT: IR+AO Rotation velocity at galaxy center 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 Sag A* in Chandra X-ray view Exhibits outbursts, but starved of fuel? 6

7 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 4414 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 7

8 Andromeda found to be far outside Milky Way another island universe : galaxy! Edwin Hubble in 1924 identified Cepheids in Andromeda (M31) 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) 8