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 and planets • Lecture 9: Our king: The Sun • Lecture 10: Shades of colors: so many stars… • Lecture 11: The life of a : from its birth to its death • Lecture 12: The quest for another Earth: extrasolar planets The Milky-Way, and our Universe • Lecture 13: The cosmic carrousel: galactic structure & 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 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 (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 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 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? - -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. a rigid body 2. a system with concentrated mass…

68 The Department of Physics and Astronomy, The University of North Carolina at Chapel Hill Rotation curve of Milky Way

Doppler measurements of the rotation curve

Wikipedia Brews Ohare Dl V = r l c 69 Rotation Curve of Spiral Galaxies

If we measure the Doppler shift of the galaxy along the red line, we would see a spectra like this…

70 National Taiwan Normal University Kuan Chen Dark Matter in Galaxy Halos • Galaxies rotate like solid spheres, not Keplerian.

GM(< r) V 2 = V r

Keplerian 1/r1/2

r National Taiwan Normal University Sébastien R.A Foucaud M 1 • For V=const, need M(

• Yields dark matter = 5 x stellar mass 71 Dark Matter in spiral galaxies

• A galaxy like the Milky Way or Andromeda has a 10 total visible mass of about 610 Msun. • The rotation velocity is ~220 km/sec • The radius about ~30 kpc • Newton: GM v2 R v = Þ M = rot rot R G

11  total mass: 3.310 Msun  ~5 times more mass than visible

72 Dark Matter in spiral galaxies Observations of the mass in spiral galaxies suggest: – Majority of masses in spiral galaxies contained in a spherical halo that surrounds the disk of our galaxy – 90% of mass of spiral galaxies do not emit light: Dark Matter – Only about 10% of the mass in the spiral galaxies in luminous form concentrated in the disk of the galaxies…

90% 10%

73 What is Dark Matter?

• WE DON’T KNOW!

• Ordinary matter = baryons • MACHOs (MAssive Compact Halo Objects) – Brown Dwarfs, black holes, neutron stars – Ruled out due to lensing • Nonbaryonic matter – Neutrinos (too light) – WIMPs (Weakly Interacting Massive Particles) – Interact weakly – Very small

74 The Universe

credit: NASA

75 Dark Matter and Galaxies

• Dark Matter = primary gravity source in galaxy formation • Clustering = result of dark matter • Matter arranged in huge chains (or walls) and large voids

76 Dark Matter and Galaxies

Simulation courtesy of Springel, White, and Hernquist

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National Taiwan Normal University Sébastien R.A Foucaud

This work is from The Department of Physics and Astronomy, The University of North Carolina at Chapel Hill http://www.physics.unc.edu/~evans/pub/A31/Lecture21-Milky-Way/rotation- comparison.jpg It is used subject to the fair use doctrine of: •Articles 52 & 65 of Taiwan Copyright Act. The "Code of Best Practices in Fair Use for OpenCourseWare 2009 (http://www.centerforsocialmedia.org/sites/default/files/10-305-OCW-Oct29.pdf)" by A Committee of Practitioners of OpenCourseWare in the U.S. The contents are based on Section 107 of the 1976 U.S. Copyright Act

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