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Galaxies Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Quotes & Cartoon of the Day “The great spirals... apparently lie outside our stellar system.” Copyright © 2012 by Sidney Harris. -- Edwin Powell Hubble “Theories crumble, but good observations never fade.” -- Harlow Shapley “Is it not careless to become too local when there are four hundred billion stars in our galaxy alone.” -- A. R. Ammons Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Announcements • • SS Homework due 11/19 3rd midterm 12/3 • • I will drop the lowest midterm grade Minor schedule update posted Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Last Class • Stellar Evolution ctd. • • Red Giants and Supergiants Endgame • • • • Low mass stars— planetary nebulae, white dwarfs High mass stars — supernovae, neutron stars, black holes Binaries & Clusters (time permitting) Galaxies • • • What’s a Galaxy? Galaxy types LT Galaxy classification Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 This Class • Stellar Evolution wrapup. • • • Binaries & Clusters Galaxies • • • • Black holes What’s a Galaxy? Galaxy types LT Galaxy Classification Our Galaxy, the Milky Way Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 JOURNEY INTO A BLACK HOLE Journey into a Black Hole Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 ANOTHER SCENARIO (INVOLVING MORE THAN 1 STAR) Type Ia Supernovae • Ingredients : a white dwarf & a post-mainsequence companion • companion dumps material onto the white dwarf • • • Mass reaches 1.4 M☉ electron degeneracy can’t support star resulting supernova completely obliterates the white dwarf Astronomy 1 - Elementary Astronomy Artist’s Concept Image: NASA/CXC/M Weiss. LA Mission College Levine F2015 Importance of Type Ia SN • SNIa are Standard Candles • • • very consistent conditions light output very predictable always have same peak luminosity Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice What is the fate of a 10-solar mass star? A. Type Ia supernova B. Type II supernova C. white dwarf Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 What is the fate of a 5 solar mass remnant core after a Type II supernova has occurred? A. neutron star B. black hole C. white dwarf D. planetary nebula Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 If your black hole research spaceship approached the site of very massive star that had gone supernova, what would happen? A. It would inevitably get sucked into the black hole with no possibility of escape. B. It would detect the gravitational pull of the black hole and be able to go into orbit around it. C. It would be unable to locate the black hole because it’s, well, black. D. It would be repelled by the black hole. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stars in Groups Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 Binaries & Clusters • • Single stars are not common! 1/2-2/3 stars are in pairs (binaries) or larger multiple star systems Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 BINARY STARS & MULTIPLE STAR SYSTEMS Binary Stars • 2 stars orbiting around their common center of mass • Important • masses of component stars can be determined from orbit • other properties can be indirectly estimated • e.g. radius and density Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Mass Transfer • If stars are close, gravity tidally distorts outermost layers • • can exchange mass can lead to novae & type Ia supernovae Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice Suppose you discover two stars that appear to be very close to each other in terms of angular separation. You measure the stellar parallax for each and find one to be at 4 pc and the other at 10 pc. Have you discovered a binary star system? A. Yes B. No C. Maybe Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 HDE 226868, a very high mass star, orbits Cygnus X-1, the first widely accepted black hole. The fact that Cygnus X-1 was in a binary system was key in making the initial argument that it was a black hole. This was because _____. (use your knowledge of binaries and black holes to reason this out) A. HDE 226868 was observed falling into Cygnus X-1 B. the light from HDE226868 illuminates Cygnus X-1 allowing it to be seen C. the orbit of HDE226868 allows the mass of Cygnus X-1 to be determined Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 CLUSTERS Stars in Groups: Clusters • Stars come in singles & binaries but also in larger groups. Clusters of stars are groups of stars that formed at the same time, from the same molecular cloud. • • • similar age similar metallicity Cluster HR diagrams change as the cluster ages Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stars in Groups: Clusters • Open Clusters • • Sparse & small • Loosely grouped & move through space together but can be disrupted • Usually only a few hundred to a few thousand stars “Young” subsequent generation metal-rich stars • Appear bluer (Population I) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Stars in Groups: Clusters • Globular Clusters • Spherical collection of stars gravitationally bound together • dense • hundreds of thousands to millions of stars, packed most densely in the center. • Orbit the galactic core in the halo (not in the plane of the galaxy) • “Old” first generation metal-poor stars • Appear redder (Population II) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice In a stellar cluster, all the members have ______. A. the same spectral type B. similar age C. Both D. Neither Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 You observe two similar star clusters, which you call Wally and Eddie. You collect enough data on each cluster to plot its H-R diagram. The brightest main sequence star in Wally is almost 10 times brighter than than the brightest main sequence star in Eddie. What do you conclude? A. Wally is larger than Eddie B. Eddie is larger than Wally C. Eddie is younger than Wally D. Wally is younger than Eddie Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Interstellar Medium Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 The Interstellar Medium (ISM) • • material which fills space between stars approximately 15% of the visible matter in the Milky Way is ISM • • • Mostly Hydrogen and Helium (99%) small fraction dust/PAHs • • nebulae polycyclic aromatic hydrocarbons trace amounts of many other compounds Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 ISM • • 75% H, 25% as He. average density ~1 atom per cc • • air ~30,000,000,000,000,000,000 molecules per ccc Molecular Clouds • • • • Orion Nebula — emission Cold clouds of neutral atomic or molecular gas & dust Horsehead Nebula, dark Witch Head Nebula — reflection dark nebulae reflection nebulae (blue) HII regions • • Hot ionized hydrogen bright, usually pink emission nebulae Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Galaxies: Classification, Spiral Structure, Oddballs Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 What is a galaxy? • large-scale collections of stars, gas, and dust • galaxies & intergalactic medium make up the universe • held together by gravity • organized around a galactic nucleus • elliptical or spiral in shape • small % irregular Astronomy 1 - Elementary Astronomy A Distant Cluster of Galaxies Image Credit: FORS1, 8.2-meter VLT, ESO LA Mission College Levine F2015 Galaxies come in many shapes & sizes Credit: NASA; ESA; G. Illingworth, D. Magee, and P. Oesch, University of California, Santa Cruz; R. Bouwens, Leiden University; and the HUDF09 Team Hubble eXtreme Deep Field (XDF) showing 5500 galaxies Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 DISCOVERY OF GALAXIES IN WHICH OUR WORLD BECAME SMALLER ANOTHER TIME Galaxies • Until early 20th century thought to be “spiral nebulae” • By 1920 some scientists began to argue they might be “island universes” outside our own system M51 -- the Whirlpool galaxy Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Edwin Hubble • • 1920 so-called Great Debate • • Shapley-Curtis debate • Heber Curtis — spiral “nebulae” are external galaxies • no “winner” Harlow Shapley — universe is 1 galaxy, spiral nebulae are mostly gas Edwin Hubble • • final “proof" 1923-26 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Edwin Hubble Image Credit: Caltech • Used new 100” telescope on Mount Wilson • observed individual stars in in M31 (the Andromeda Galaxy) • identified Cephied variable stars which gave a distance to M31 well outside the Milky Way • also developed the currently used system of galaxy classification & discovered Hubble’s Law Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 GALAXY CLASSIFICATION Three main types Whirlpool Galaxy (M51) • Spirals NASA and European Space Agency NGC 1132 • Ellipticals Large Magellenic Cloud NASA, ESA, and the Hubble Heritage Collaboration • Irregulars Eckhard Slawik Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Morphological Classification Scheme NASA/ESA Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Elliptical Galaxies • Elllipsoidal shape & smooth brightness profile • ~20% of observed galaxies • 10s of millions to > 1 trillion stars • older, red, low-mass stars • sparse interstellar medium • minimal star formation activity Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Spirals • Round bulge, flat disk, spiral arms and spherical halo • Divided into “normal” (S) and “barred” (SB) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Spirals • together make 77% of observed galaxies • Younger blue stars in arms • Older red stars in bulge and halo Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Sa Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Sb Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Sc M99 NOAO/AURA/NSF Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 SBa Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 SBb NGC 1365 APOD Nov 24 2012 SN2012fr discovered 10/27/12 type Ia supernova -- explosion of a white dwarf star. Image Credit & Copyright: Martin Pugh Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 SBc NGC 7479 ESA/Hubble & NASA Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Irregular Galaxies • • Denoted Irr • about 3% of observed galaxies • Mostly young, blue stars Lack symmetry Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WARM-UP QUESTION A galaxy that appears to be populated by mostly red stars, likely _____. A. never had blue stars in the galaxy. B. had blue stars that are not present anymore but were at one time long ago. C. has been around long enough for blue stars to all evolve into the red main sequence stars we see. D. never contained enough gas to have blue stars develop. E. as blue stars that are being blocked by dust. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 LT GALAXY CLASSIFICATION A galaxy that appears to be populated by mostly red stars, likely _____. A. never had blue stars in the galaxy. B. had blue stars that are not present anymore but were at one time long ago. C. has been around long enough for blue stars to all evolve into the red main sequence stars we see. D. never contained enough gas to have blue stars develop. E. as blue stars that are being blocked by dust. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Let’s Practice How would you classify the Milky Way? NASA/JPL-Caltech/R. Hurt A. SBbc B. Sb C. S0 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The centers of most spiral galaxies appear redder than the arms. The most likely explanation for this is _____. A. young blue stars are primarily in the arms and old red stars in the bulge B. nuclear reactions in the center are creating heat C. the black hole in the center is glowing red Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Elliptical galaxies contain mostly red stars. What can you conclude about the rate of star formation in elliptical galaxies? A. Few to no new stars are forming. B. Many new stars are forming. C. There is not enough information to conclude anything. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 THE PUZZLE OF SPIRAL STRUCTURE AND ITS SOLUTION The Winding Dilemma • 1925 Bertil Lindblad • stars can not stay arranged in a spiral shape • arms “wind up” • implies few spiral galaxies • • but we see many • Lindblad proposed spiral structure actually regions of increased density the “winding dilemma” Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Density Waves • Therefore something other than a fixed pattern of stars must account for spiral shape • • The stars must move THROUGH the pattern Think of a traffic jam Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Density Wave in a Galaxy • Lin & Shu (1965) developed a plausible spiral density wave theory • The stars and gas move through the spiral structure • Gas is compressed and star formation is triggered Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Slightly Silly Video Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 We live in a Galaxy: The Milky Way Astronomy 1 — Elementary Astronomy LA Mission College Spring F2015 INTRO TO THE MILKY WAY The Milky Way • • • Our home galaxy A barred spiral galaxy From our solar system, we see this... Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Milky Way over the VLT Image Credit: ESO (Yuri Beletsky) Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Structure of the Milky Way • Looking through the disk from inside and combining the 2-D data with distance information allows us to construct a model of what the Milky Way looks like from outside... Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Edge-on Model http://woodahl.physics.iupui.edu/Astro105/ Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Face-on Model Image Credit NASA/JPL-Caltech/R. Hurt Astronomy 1 - Elementary Astronomy LA Mission College Image Credit NASA/JPL-Caltech/R. Hurt Levine F2015 Structure of the Milky Way • Bulge: spherioidal • • • • • about 6000 ly diameter Densely packed old red stars Bar Disk: flat • • about 90,000 ly x 900 ly • Sun about 24,000 ly from center Stars and interstellar gas and dust, including young stars Halo: Spheroidal • • about 300,000 ly diameter Image Credit: R.J. Hall old stars, globular clusters, dark matter, hot gas Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 3D Model Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WHAT’S IN THE MW? Milky Way Recipe 300 ± 100 billion stars at least 1983 planets Interstellar Medium (ISM) ~ 1010 M⊙◉☉ Supermassive Black Hole ~ 4-4.5 x 106 M⊙◉☉ Dark Matter to account for a total mass of 1-1.5 x 1012 M⊙◉☉ Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Where is the Interstellar Medium? Milky Way Galaxy • Interstellar Medium = ISM • Everywhere between stars • not uniformly distributed, denser in bar and arms Image Credit NASA/JPL-Caltech/R. Hurt Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 THE GALACTIC CENTER The Galactic Center • • • Images about 8° across. GC in upper left Entirely obscured in visible light First explored using radio astronomy later further explored with IR astronomy Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Galactic Center • The GC is very wierd place • WAAAY down inside the bulge • This image about 3° (1400 ly) across • Sgr A* location of black hole Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Supermassive BH in MW Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 The Galactic Center • stellar orbits in the central 3 ly • evidence for a supermassive black hole, with mass 4 million times the mass of the Sun. Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 DARK MATTER •The data (blue curve) indicate the stars in the outer Galaxy have higher orbital speeds than can be explained by the known mass. •Dark matter that extends to great distances from the galactic center provides the gravitational force needed to give the outer stars these higher speeds. Predicted Keplerian orbit based on cataloged content Actual rotation of Milky Way Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 http://www.astro.ufl.edu/~guzman/ast1002/class_notes/Ch15/gal_rotation.gif What is Dark Matter? • Rotation curve provides evidence mass • But we don’t see it as stars, dust, gas • We call it dark matter because we haven’t directly detected it through observing light • We don’t really know what it is made out of, we just know where it is and how much of it there is! • In the Milky Way, most is in the halo, and possibly an extended disk • 6 x1011 to 3 x 1012 M⊙◉☉ Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 WRAP-UP Topic for Next Class • Hubble’s Law & the Expansion of the Universe Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Reading Assignment • • Astro:10&11 Astropedia:15&16 Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015 Homework • HW SS Due Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015