Introduction to Astronomy Prof. Sébastien R. A. Foucaud Department of Earth Sciences National Taiwan Normal University Unless noted, the course materials are licensed under Creative Commons 1 Attribution-NonCommercial-ShareAlike 3.0 Taiwan (CC BY-NC-SA 3.0) Credits: Chris Hetlage 2 Syllabus Astronomical techniques • Lecture 1: Finding its way on the night… • Lecture 2: Moving blindly and seeing the light… • Lecture 3: Eyes better than my eyes: the telescopes The solar system • Lecture 4: Home: Earth • Lecture 5: Our close friend: The Moon • Lecture 6: Our neighborhood: Rocky Planets • Lecture 7: The good Monsters: Giant Planets • Lecture 8: Dwarf Planets, minor bodies and scenario of solar system formation Stars and planets • Lecture 9: Our king: The Sun • Lecture 10: Shades of colors: so many stars… • Lecture 11: The life of a star: from its birth to its death • Lecture 12: The quest for another Earth: extrasolar planets The Milky-Way, galaxies and our Universe • Lecture 13: The cosmic carrousel: galactic structure & Galaxy formation • Lecture 14: Hubble, the expansion of the Universe and the Big-Bang Theory • Lecture 15: Einstein and the relativity 3 Lecture 13 The cosmic carrousel: galactic structure 4 Galaxies Spiral Galaxy NGC 253 Almost Sideways Credit & Copyright: Jean-Charles Cuillandre (CFHT) Hawaiian Starlight, CFHT APOD: 2003 May 25 • Star systems like our Milky Way •Few million to tens of billions of stars. • Large variety of shapes and sizes 5 Charles Messier (1730-1817) 6 M31 M51 M82 M82 New General Catalogue (NGC)/Johan Ludvig Emil Dreyer, William 7 Herschel, John Dunlop, Charles Messier M104 Messier Catalog, 1751 M31: The Andromeda Nebula 8 M51: The Whirlpool Galaxy 9 M82: An Exploding Galaxy 10 M1: The Crab Nebula 11 M57: The Ring Nebula 12 The Spiral Nebulae? • Nature unknown • Avoided the Milky Way • Immanuel Kant (1724 – 1804) speculated about “Island Universes”. – Spiral Nebulae are other Milky Ways – Very distant and external to our Galaxy • 3rd Earl of Rosse (William Parsons) (1800 – 1867) built a giant reflector to observe them carefully. 13 The Leviathan of Parsonstown: 1840 183 cm (Primary mirror) 14 1920’s: The Great Debate Shapley vs. Curtis Are these nearby Or distant stellar clouds of gas? systems (galaxies) 15 ESO Projects The “Discovery” of Galaxies Edwin P. Hubble (1889-1953) Wikipedia Adabow • 1920’s: new 100in telescope built on Mt. Wilson • 1924: Hubble found cepheids in M31 beyond the Milky Way • Prove that M31 is another galaxy 16 Cepheids 17 National Taiwan Normal University Kuan Chen 70 years later: Hubble Deep Field • 10 day exposure photo! • Over 1500 galaxies in a spot 1/30 the diameter of the Moon • 1011 galaxies in the observable universe • Farthest and oldest objects are 13 billion light years away! • Space observations as a time machine 18 Heaven on Earth (Milky Way from Northern Hemisphere) Credit & Copyright: Richard Payne (Arizona Astrophotography) APOD: 2004 February 23 19 The Milky Way at 5000 Meters (Milky Way from Southern Hemisphere) Credit & Copyright: Serge Brunier APOD: 2008 January 4 20 The Milky Way from Cerro Tololo Inter-American Observatory in the Chilean Andes. (NOAO/AURA Photo) 21 The Milky Way •A faint band goes across the sky •Galileo showed that the band was made of individual stars •We are inside of the galaxy, so its hard to see what the overall structure of it is 22 Edge-on View of the Milky Way halo globular star clusters & individual stars M104 bulge sun stars, gas & dust disk stars, gas & dust 28,000 light years 1,000 light years 100,000 light years National Taiwan Normal University 23 Sébastien R.A Foucaud Milky Way Illustrated Illustration Credit & Copyright: Mark Garlick (Space-art) APOD: 2005 January 4 24 Other Galaxies • Over 100 billion in the observable universe • Many different shapes and sizes 25 Irregulars http://cas.sdss.org/dr5/en/ Properties of Galaxies Property Spirals Ellipticals Irregulars 9 11 5 13 8 10 Mass/M 10 - 4x10 10 - 10 10 - 3x10 8 10 5 11 7 9 Luminosity/L 10 - 2x10 3x10 - 10 10 - 3x10 Diameter 16x103 - 8x105 3x103 - 7x105 3x103 - 3x104 (light years) Population 77% 20% 3% 27 Spiral galaxies M51 M104 28 M31: The Andromeda Galaxy Credit & Copyright: Robert Gendler (robgendlerastropixs.com) APOD: 2004 July 18 Disk: Gas, dust, young and old stars Bulge: Old stars Orbits of Stars • Disk stars go around the center of the galaxy – Also oscillate above and below the disk • Halo and bulge stars move around randomly – Can be very far away from the disk • Study orbits of stars to determine mass of the galaxy 31 M51: The Whirlpool Galaxy in Dust and Stars Credit: N. Scoville (Caltech), et al., Hubble Heritage Team, NASA APOD: 2006 February 19 32 Edge-On Galaxy NGC 5866 Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Acknowledgment: W. Keel (U. Alabama) APOD: 2006 June 12 33 M64: The Sleeping Beauty Galaxy Credit: NASA and the Hubble Heritage Team (AURA/STScI), S. Smartt (IoA) & D. Richstone (U. Michigan) et al. 34 APOD: 2004 February 11 Barred Spiral Galaxy NGC 1300 Credit: Hubble Heritage Team, ESA, NASA APOD: 2006 August 27 35 Spiral Arms M74 36 So what causes spiral arms? National Taiwan Normal University Kuan Chen It happens too fast: Universe ~10-15 billion years, Arms so tightly wrapped, therefore invisible! 37 Density waves 38 National Taiwan Normal University Kuan Chen Spiral arms are patterns • According to the density-wave theory, spiral arms are created by density waves that sweep around the Galaxy • The gravitational field of this spiral pattern causes stars and gas to slow down near the arm • This compresses the interstellar clouds, triggering the formation of stars • The entire arm pattern rotates around the Milky Way once every 500 million years 39 Spiral arms and density waves Wikipedia: Author Unknown, User: Dbenbenn / Mysid 40 Wikipedia Ingo Berg Elliptical galaxies M32 M110 42 Elliptical galaxies E0 (M1050 E3 (NGC4365) E6 (NGC3377) • little interstellar gas and dust • very little star formation • mainly old stars (billions of years old) • few or no young stars (millions of years old) • Random velocities of stars 43 National Taiwan Normal University Kuan Chen Irregular Galaxies I Zwicky 18 The Antennae 44 The Large Cloud of Magellan Credit & Copyright: Wei-Hao Wang (IfA, U. Hawaii) APOD: 2006 May 10 The Small Cloud of Magellan Credit & Copyright: Josch Hambsch, Robert Gendler APOD: 2005 June 17 Galaxies love to live in group The Local Group 47 Wikipedia Richard Powell Galaxy Group HCG 87 Credit: GMOS-S Commissioning Team, Gemini Observatory APOD: 2005 July 16 48 The Perseus Cluster of Galaxies Credit: Jim Misti (Misti Mountain Observatory) APOD: 2004 October 25 49 The Coma Cluster of Galaxies Credit & Copyright: Jim Misti (Misti Mountain Observatory) APOD: 2006 March 21 50 Large Scale Structure 51 Galaxy Facts Grouping: • Spiral galaxies in small groups • Ellipticals in large clusters Size (decreasing order): • Giant elliptical galaxies (clusters) • Spiral galaxies • Small ellipticals (near large spirals) 52 Galaxies quite close to each other! Galaxy size ~ 100 kpc Separation between galaxies ~ 1 Mpc Size/Separation > 0.1 ! For stars, Size/Separation ~ 10-7 Galaxies interact and collide very often! 53 Galaxy interactions • Galaxies rarely in isolation (In the past even closer) • Take hundreds of millions of years to be completed • Rip stars out of galaxies, producing tidal tails • Gas settles in the center and forms many new stars • Disturb gas in and between galaxies, producing starbursts • Randomize stellar orbits leading to the formation of elliptical galaxies 54 Spiral Galaxies in Collision Credit: Debra Meloy Elmegreen (Vassar College) et al., & the Hubble Heritage Team (AURA/ STScI/ NASA) APOD: 2004 November 21 55 Antennae galaxy 56 56 Hubble Space Telescope – WFPC2 + ACS 57 Milky Way eating neighbors 58 Galactic cannibalism Giant elliptical in the cluster center gets bigger by eating neighbors 59 Galaxy Formation • No stars formed yet so no direct observations – Extensive use of computer simulations • Assume that Hydrogen and Helium gas spread (almost) uniformly throughout the universe • Rotation of the galactic disks established after the first generation of stars • Galaxy formed from a Protogalactic Cloud • Multiple clouds • Protogalactic Cloud Differences – Protogalactic spin might have varied – Protogalactic density might have varied 60 Galaxy Formation National Taiwan Normal University Kuan Chen 61 National Taiwan Normal University Kuan Chen Galactic Recycling • Stars don’t form uniformly in the galaxy • Stars form in the spiral arms of galaxies - Arms “blue” while other parts “red” • Spiral density waves probably responsible • Stars dump material into the ISM as they die • Gravity drags gas and cools it • Large gas clouds formed, from which stars can form again 62 Galaxy Formation • This picture of galaxy formation is incomplete • Mergers, collisions, and interactions between galaxies very important in their formation, • Particularly in the early stages of the Universe • Anything else? (Black holes) 63 Galaxy growth via interactions • Galaxies initially form from mergers of several gas clouds • Galaxies then are changed by interactions • Galaxies grow gradually by galactic cannibalism • Interactions disturb gas leading to starbursts • Collisions randomize stellar orbits leading to the formation of elliptical galaxies 64 Galaxy growth via interactions This work is licensed by Andrey Kravtsov/The Center for Cosmological Physics for the use of “Course Database 65 of General Education TW” ONLY. The copyright belongs to the above mentioned entity and GET does not have the right to sub-license. Copyright privileges have to be negotiated with the copyright owner(s) for separately. Galaxy Formation • Bottom-to-top formation? 6 - Objects of globular cluster size ~ 10 M formed first; then clustered into bigger galaxies, groups, etc. • Top-to-bottom formation? - Supercluster-size objects formed first, and smaller scales later 66 Galaxy Formation Top-to-bottom time Primordial gas Bottom-to-top National Taiwan Normal University Sébastien R.A Foucaud 67 Rotation Curve and Mass Rotation curves of : 1.