06 Galaxies Mc Neely


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06 Galaxies Mc Neely

  1. 1. Astronomy Topic 06 : Galaxies Stephen’s Quintet
  2. 2. Galaxies <ul><li>Galaxy : A group of millions or billions of stars, gas, and dust held together by gravity </li></ul><ul><li>Our sun and all visible stars are members of our galaxy, the Milky Way </li></ul>
  3. 3. Our Galaxy <ul><li>The Milky Way is visible as a band of light crossing the sky during summer and winter </li></ul><ul><li>Represents the concentrated light of the billions of stars in our galaxy </li></ul><ul><li>At night, we witness the view from within our galaxy </li></ul>
  4. 4. Milky Way Galaxy <ul><li>A disk of stars that contains 100-200 billion stars </li></ul><ul><li>100,000 light years in diameter, about 3000 LY thick </li></ul><ul><li>The center of the Milky Way (nuclear bulge), swells to about 10,000 LY thick </li></ul>
  5. 5. Milky Way Diagram http://zebu.uoregon.edu/~imamura/123/images/mw-schematic.jpg
  6. 6. Milky Way
  7. 7. Infrared Milky Way (COBE) http://www.astro.psu.edu/users/niel/astro1/slideshows/class21/slides-21.html The view from within, in IR light
  8. 8. Sun and Galaxy <ul><li>Sun located about 2/3 distance away from the center (30,000 LY) </li></ul><ul><li>The entire Milky Way rotates around its center </li></ul><ul><li>Sun orbits the center of the galaxy at 563,000 mph </li></ul><ul><li>One galactic revolution takes 220 million years </li></ul>
  9. 9. Sun’s Revolution http://www.envirotruth.org/images/graphics/suns_path.jpg
  10. 10. Milky Way, a Spiral Galaxy <ul><li>Spiral galaxy, most are concentrated in a central nucleus </li></ul><ul><li>Spiral arms of stars wind outward from the nucleus </li></ul>M101
  11. 11. Milky Way Map http://members.nova.org/~sol/chview/milkyway.jpg
  12. 12. Star Clusters : Open Clusters <ul><li>A few dozen to thousands of stars loosely bound together by gravity </li></ul><ul><li>Found mainly in the galaxy’s disk and spiral arms </li></ul><ul><li>More than 1000 have been discovered in the MW </li></ul><ul><li>Young stars that recently formed from nebulosity </li></ul>Jewel Box open cluster (NGC 4755)
  13. 13. Star Clusters : Globular Clusters <ul><li>Huge, concentrated balls of thousands to millions of stars </li></ul><ul><li>Found in galactic halo, a spherical region centered on the nucleus </li></ul><ul><li>Contain the oldest known stars </li></ul><ul><li>About 150 globular clusters have been discovered </li></ul>Omega Centauri, globular cluster (NGC 5139)
  14. 14. Cluster Summary Type Open Cluster Globular Cluster Stars Dozens to thousands (Population I) Hundreds to millions (Population II) Location Within galactic disk Orbit galaxy in halo Age Young, thousands to millions of years Among oldest known stars (billions of years)
  15. 15. Open Cluster HR Diagrams <ul><li>This HR diagram plots the stars for many open clusters </li></ul><ul><li>As clusters age, their main sequence stars appear lower on the HR diagram </li></ul><ul><li>Pleiades are younger than M67 </li></ul>
  16. 16. Open Clusters Pleiades—M45 M67 Which cluster is oldest? Note the star colors of the main stars in each cluster
  17. 17. Globular Cluster M55 <ul><li>Colors indicate temperatures, red (cool) to blue (hot) </li></ul><ul><li>The “turn off” area on the main sequence represents the cluster’s age </li></ul>
  18. 18. Dark Matter <ul><li>Galaxies consist of ordinary stars, gas, and dust </li></ul><ul><li>Observed motions of stars in a galaxy indicate unseen (dark) matter </li></ul><ul><li>Due to dark matter, galaxies rotate faster than the observable matter allows </li></ul><ul><li>Visible galaxies surrounded by large, nonluminous galactic halos </li></ul>http://www.pparc.ac.uk/Ps/aac/images/image33.gif
  19. 19. Dark Matter in NGC 3198 http://bustard.phys.nd.edu/Phys171/lectures/ngc3198_opt_rad_rot.jpg
  20. 20. Between the Stars <ul><li>Space between the stars in a galaxy is a vacuum, or empty space </li></ul><ul><li>Also termed interstellar medium </li></ul><ul><li>Matter between the stars is of gas and dust </li></ul><ul><li>Interstellar matter 99% gas, 1% dust </li></ul><ul><li>Gas consists of 75% hydrogen and 25% helium </li></ul><ul><li>Interstellar dust similar in size to cigarette smoke </li></ul><ul><li>In spiral galaxies, gas and dust is concentrated in the disk and spiral arms </li></ul>
  21. 21. Molecular Clouds <ul><li>> 100 interstellar molecules have been detected in molecular clouds between stars </li></ul><ul><li>Water vapor, amino acids, and other organic molecules (urea, alcohol) </li></ul><ul><li>Ingredients of life can be found in the galaxy’s molecular clouds </li></ul><ul><li>Cosmic origin of life? </li></ul>
  22. 22. Nebulas <ul><li>Historically, a nebula meant any type of hazy, glowing patch of light in the night sky </li></ul><ul><li>Andromeda Galaxy once termed the Andromeda Nebula </li></ul><ul><li>Today, nebula means interstellar gas and dust </li></ul>
  23. 23. Emission Nebulas <ul><li>Emission nebulas glow due to excitement from nearby stars </li></ul><ul><li>Also called diffuse nebulas or HII regions </li></ul><ul><li>Orion Nebula (M42), famous example of an emission nebula (next slide) </li></ul>
  24. 26. Pillars of Creation (M16) <ul><li>In this iconic photo from the Hubble Space Telescope, a small portion near the center of M16, the Eagle Nebula, is revealed </li></ul><ul><li>Note the pink, newly formed stars within the nebula </li></ul>
  25. 27. Dark Nebulas <ul><li>Dark nebulas, or absorption nebulas, molecular clouds that block the light of distant stars </li></ul><ul><li>E.E. Barnard used photography to map the galaxy’s dark nebulas in the early 20th century </li></ul><ul><li>Dark nebulas today bear “B” numbers in his honor </li></ul>
  26. 28. Barnard’s S Nebula http://www.astropix.com/HTML/D_SUM_S/B72.HTM A dark nebula represents interstellar dust that blocks the light of stars from behind
  27. 29. Horsehead Nebula Famous dark nebula (B33) located near the Belt of Orion
  28. 30. Star Populations <ul><li>Walter Baade (1944) divided a galaxy’s stars into two categories: </li></ul><ul><li>Population I </li></ul><ul><ul><li>Hot, young, and luminous </li></ul></ul><ul><ul><li>Found in galactic disk </li></ul></ul><ul><ul><li>Contain heavy elements beyond H and He </li></ul></ul><ul><li>Population II </li></ul><ul><ul><li>Old, cool stars, some first stars in universe </li></ul></ul><ul><ul><li>Found in globular clusters and galactic nucleus </li></ul></ul><ul><ul><li>Almost all H and He </li></ul></ul>
  29. 31. Catalogs <ul><li>Messier Catalog of 110 objects (1784) by French astronomer Charles Messier </li></ul><ul><li>Dreyer’s New General and Index Catalogs of thousands of objects (1895-1908) </li></ul><ul><li>NGC contains 7840 objects </li></ul><ul><li>“ M” or “NGC”, or “IC” numbers </li></ul><ul><li>Objects, mainly galaxies, star clusters, and nebulae </li></ul>
  30. 32. Messier Catalog All of the Messier objects are shown in this montage M1 starts the upper left, M110 ends the lower right
  31. 33. Formation of the Milky Way <ul><li>Milky Way appears to be about 13 billion years old </li></ul><ul><li>MW likely represents one of the original galaxies created after the Big Bang </li></ul><ul><li>Sun and planets are 4.5 billion years old </li></ul><ul><li>Big Bang origin of universe 13.7 bya </li></ul>
  32. 34. Other Galaxies <ul><li>Until 1924, Milky Way was the “universe” </li></ul><ul><li>Edwin Hubble proved that galaxies other than our Milky Way exist </li></ul><ul><li>Hubble used Cepheid variable stars to measure the distances to galaxies </li></ul><ul><li>Hubble also photographed stars in the Andromeda “Nebula” </li></ul><ul><li>The universe contains an estimated 100 billion galaxies. Each of these galaxies contains about 100 billion stars </li></ul>
  33. 35. Standard Candles <ul><li>An astronomical object whose absolute magnitude is know from its observed characteristics </li></ul><ul><li>Can be used to determine distances to galaxies up to 10 million LY from earth </li></ul><ul><li>Examples: </li></ul><ul><ul><li>Cepheid variable stars </li></ul></ul><ul><ul><li>Globular clusters </li></ul></ul><ul><ul><li>Supernovas </li></ul></ul>
  34. 36. Andromeda Galaxy <ul><li>Our nearest large neighbor </li></ul><ul><li>Similar in size and shape to Milky Way </li></ul><ul><li>Andromeda Galaxy is visible to the naked eye as a glowing spot in the constellation of Andromeda </li></ul><ul><li>2.3 million light years distant (wave!) </li></ul>
  35. 37. Andromeda Galaxy (M31, M32, M110)
  36. 38. Andromeda Constellation Locate M31 and M33
  37. 39. Triangulum Galaxy (M33)
  38. 40. M33 The pink glow of emission nebulas can be seen in this photo
  39. 41. Virgo <ul><li>Virgo Supercluster </li></ul><ul><li>About 200 galaxies are visible in small telescopes </li></ul><ul><li>Galaxies range from Ursa Major through Coma Berenices to Virgo </li></ul>Sombrero Galaxy
  40. 42. Center of Virgo Cluster Virgo Cluster near M84, M86 M86
  41. 43. Sombrero Galaxy (M104) from HST
  42. 44. Sheets and Voids <ul><li>Superclusters are located in thin sheets of galaxies </li></ul><ul><li>Sheets border empty voids </li></ul><ul><li>Voids resemble gigantic bubbles </li></ul><ul><li>The universe resembles a sponge </li></ul>
  43. 45. Large-Scale Structure of the Universe http://www.astro.princeton.edu/~cen/PROJECTS/p1/DARKallz0.jpeg Sheets & Voids: http://heasarc.nasa.gov/docs/cosmic/sheets_voids.html
  44. 46. Active Galaxies (AGN) <ul><li>An active galaxy emits large amounts of energy from its nucleus </li></ul><ul><li>AGNs exhibit jets of hydrogen racing outward along an axis </li></ul><ul><li>Massive black holes? </li></ul><ul><li>Mysterious quasars might represent extremely active galaxies </li></ul>
  45. 47. Galactic Cannibalism <ul><li>Galaxies can merge together to form larger galaxies </li></ul><ul><li>Elliptical galaxies may be the result of multiple galaxy collisions </li></ul>NGC 2207 (left) and IC 2163 (HST)
  46. 48. Quasars <ul><li>Resemble faint stars, are strong radio sources </li></ul><ul><li>Acronym for Quasi-Stellar Radio Source </li></ul><ul><li>Small objects, yet emit energy egual to thousands of galaxies combined </li></ul><ul><li>Most distant and powerful objects known </li></ul><ul><li>Might represent early stage of galaxy growth </li></ul><ul><li>Seyfert galaxies are active galaxies with nuclei that resemble quasars </li></ul>
  47. 49. 3C 273-Quasar HST image of 3C 273 showing disk details (quasar blocked) 3C 273 Starfield in Virgo 3C 273 is one of the first identified quasars, it resembles an 11 th magnitude star in Virgo and is visible in small amateur telescopes