07 Universe Mc Neely


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  • FIGURE 18-22 Dimmer Distant Supernova (a) These Hubble Space Telescope images show the galaxy in which the supernova SN 1997ff occurred. This supernova, more than 10 Bly away, was dimmer than expected, indicating that the distance to it is greater than the distance it would have if the universe had been continually slowing down since the Big Bang. This supports the notion that an outward (cosmological) force is acting over vast distances in the universe. The arrow on the first inset shows the galaxy in which the supernova was discovered. The bright spot on the second inset shows the supernova by subtracting the constant light emitted by all the other nearby objects. (b) The distances and brightnesses of many very distant supernovae are plotted on this diagram. The location of the most distant supernovae in the upper region strongly indicates that the universe has been accelerating outward for the past 6 billion years. (a: Adam Riess, Space Telescope Science Institute, NASA)
  • FIGURE 18-14 The Observable Universe This diagram shows why we only see part of the entire universe. As time passes, this volume grows, meaning that light from more distant galaxies reaches us. The galaxies we see at the farthest reaches of our telescopes’ resolving power are as they were within a few hundred million years after the Big Bang (see inset ). These galaxies, formed at the same time as the Milky Way, appear young because the light from their beginnings is just now reaching us. The radius of the cosmic light horizon is equal to the distance that light has traveled since the Big Bang. Because the Big Bang occurred about 13.8 billion years ago, the cosmic light horizon today is about 13.8 billion light-years away in all directions. Inset: This image of the Hubble Deep Field shows some of the most distant galaxies we have seen. (inset: Robert Williams and the Hubble Deep Field Team, STScI and NASA)
  • 07 Universe Mc Neely

    1. 1. Astronomy Topic 07 : The Universe http://www.pbs.org/faithandreason/media/bigbang.lg.jpg
    2. 2. Cosmology <ul><li>Cosmology : The study of the origin, present structure, evolution, and destiny of the universe </li></ul><ul><li>Two basic models </li></ul><ul><ul><li>Steady state </li></ul></ul><ul><ul><li>Evolutionary </li></ul></ul>
    3. 3. Expanding Universe <ul><li>Any model of the universe must explain its expansion </li></ul><ul><li>The universe appears to be expanding </li></ul><ul><li>The light from distant galaxies appears to be red shifted due to this expansion </li></ul><ul><li>Hubble’s Law : The further away a galaxy is, the greater its redshift is and the faster it is flying away from us </li></ul>
    4. 4. Hubble’s Law <ul><li>The (linear) relationship between a galaxies velocity of recession and its distance </li></ul><ul><li>Hubble’s Law: </li></ul><ul><li>v = Hd </li></ul><ul><li>Where v=velocity, d=distance, and H=Hubble constant </li></ul><ul><li>In a graph of distance vs. recessional velocity, H becomes the slope of the line </li></ul>
    5. 5. Hubble Diagram http://www.exo.net/~pauld/activities/astronomy/Hubblelawsn1a.gif
    6. 6. We are not the center <ul><li>Galaxies appear to be flying away from our position </li></ul><ul><li>Observers in other parts of the universe would make similar observations </li></ul><ul><li>Our corner of space isn’t special, and the laws of nature are the same everywhere in the universe </li></ul>
    7. 7. Raisin Bread Analogy <ul><li>As bread expands, each raisin (galaxy) sees the others moving away </li></ul>
    8. 8. Big Bang Theory <ul><li>BB states that the universe exploded violently into existence 13.7 billion years ago and has been expanding ever since </li></ul><ul><li>At the Big Bang, all of the matter in the universe was packed together into an infinitely small area </li></ul><ul><li>Evolutionary Model: </li></ul><ul><ul><li>The universe had a beginning, will have an end, and has evolved or changed over time </li></ul></ul>
    9. 9. Big Bang Events <ul><li>The infant universe rapidly expanded (inflation) </li></ul><ul><li>One-millionth of a second: Four forces emerge (gravity, electromagnetism, strong and weak) </li></ul><ul><li>In the first few seconds electrons, protons, and neutrons formed </li></ul><ul><li>Within minutes, the first hydrogen formed. Hydrogen was the original element. Some helium and other trace elements were also created </li></ul><ul><li>300,000 years: Cosmic Background Radiation emerges </li></ul><ul><li>300 million years later, matter sprung from energy (decoupled) forming stars and galaxies </li></ul><ul><li>The universe has been expanding ever since </li></ul><ul><li>The universe consists of 74% hydrogen, 24% helium, and 2% trace elements </li></ul><ul><li>The velocity of the universe’s expansion is increasing due to dark energy </li></ul>
    10. 10. Big Bang http://www.theage.com.au/ffximage/2006/03/17/bigbangmain_wideweb__470x238,0.jpg
    11. 11. Cartoon
    12. 12. Open or Closed Universe <ul><li>Two variations of the Big Bang exist, the open and closed universe </li></ul><ul><li>The determinant for closure is the amount of matter in the universe </li></ul><ul><li>The gravity exerted by matter can halt the universe’s expansion </li></ul><ul><li>This is one reason why dark matter is an important topic </li></ul>
    13. 13. Open Universe? <ul><li>Open Universe : The universe will expand outward forever. Eventually the universe will fade away into a cold, dark void </li></ul><ul><ul><li>Flat Universe : Universe will neither expand forever or collapse. Eventually expansion will stop (critical density) </li></ul></ul>
    14. 14. Steps in the Open Universe <ul><li>Big Bang explosion took place </li></ul><ul><li>Galaxies formed </li></ul><ul><li>Galaxies are still receding </li></ul><ul><li>Original hydrogen used up, the resulting cold, black universe will continue expanding indefinitely </li></ul>Diagrams courtesy Moch é , Astronomy, a Self-Teaching Guide , Wiley (1993)
    15. 15. Closed Universe? <ul><li>Closed Universe : In the closed universe, the universe will eventually stop expanding and begin to contract. The universe will fall back together into a Big Crunch </li></ul><ul><ul><li>Oscillating Universe : Idea that a new universe is created after each Big Bang and Crunch. The universe may expand and contract eternally creating new universes each time </li></ul></ul>
    16. 16. Steps in the Closed Universe
    17. 17. Steps… <ul><li>Big Bang occurred </li></ul><ul><li>Galaxies formed and continued to recede </li></ul><ul><li>We live in an expanding universe; galaxies are racing away from one another today </li></ul><ul><li>Galaxies will stop </li></ul><ul><li>The universe will contract; galaxies will fall back inward </li></ul><ul><li>Matter will be crunched together again (Big Crunch) </li></ul>
    18. 18. Open or Closed? http://www.astro.rug.nl/~ormel/article/open_closed.jpg <ul><li>Expand forever </li></ul><ul><li>Expansion will halt </li></ul><ul><li>Big Crunch, new Big Bang? </li></ul>(critical)
    19. 19. Oscillating? http://astrosun2.astro.cornell.edu/academics/courses/astro201/images/open_closed.gif
    20. 20. Open Universe and Dark Energy <ul><li>The study of distant white dwarf supernovae indicate that the universe is open, and that its rate of expansion is accelerating </li></ul><ul><li>Evidently a repulse force (dark energy) exists in the universe that acts contrary to gravity </li></ul><ul><li>Einstein had originally predicted a repulsive force in the universe but considered it a “blunder” </li></ul>
    21. 21. Accelerating Expansion
    22. 22. Exploding White Dwarfs <ul><li>White dwarf supernovas (type 1A) occur when a white dwarf is present in a binary star system </li></ul><ul><li>The white dwarf pulls material from its companion star eventually causing either a nova (temporary brightening) or supernova (exploding star) </li></ul><ul><li>These supernovas make good standard candles as they achieve a similar brightness </li></ul><ul><li>Observations of type 1A supernova led to the discovery of the acceleration of the universe’s expansion </li></ul>
    23. 23. Supernova 1994D <ul><li>This photo from the Hubble Space Telescope is of a supernova discovered in 1994 </li></ul><ul><li>The supernova appeared in NGC 4526, a galaxy in the constellation Virgo </li></ul>http://antwrp.gsfc.nasa.gov/apod/ap981230.html
    24. 24. Dimmer Distant Supernova <ul><li>These HST images show the galaxy in which the supernova SN 1997ff occurred. </li></ul><ul><li>This supernova was dimmer than expected. </li></ul><ul><li>The distance to such galaxies was greater than previously thought </li></ul><ul><li>An outward force, named dark energy, seems to be acting over vast distances in the universe. </li></ul>
    25. 25. Steady State Theory <ul><li>Rival of Big Bang </li></ul><ul><li>States that the universe is eternal and unchanging </li></ul><ul><li>The universe does not evolve over time and has no beginning or end </li></ul><ul><li>To explain expansion, the SS theory claims that new hydrogen is created in empty space when needed </li></ul><ul><li>SS theory is rejected because it violates conservation of energy law that prohibits the creation of new matter </li></ul>God is a Steady Stater?
    26. 26. Steps in the Steady State Universe <ul><li>Galaxies are receding, the universe is expanding, new matter is being created, new galaxies are being formed </li></ul><ul><li>The same pattern will occur. The universe maintains the same average density forever </li></ul>
    27. 27. Sir Fred Hoyle (1915-2001) <ul><li>Despite being known for coining the term “Big Bang”, Fred Hoyle was the major supporter of the Steady State theory, and he held this position until his death in 2001 </li></ul><ul><li>Hoyle, an atheist, felt that the Big Bang theory was too religious, and that it implied a creator </li></ul><ul><li>Hoyle was also known for discovering the mechanism by which elements are created in stars (nucleosynthesis) </li></ul><ul><li>Always an iconoclast, he also proposed that life came from space in the form of free-floating bacteria. This theory is known as panspermia </li></ul>
    28. 28. Big Bang vs. Steady State <ul><li>Big Bang </li></ul><ul><ul><li>The universe had a beginning and will have an end </li></ul></ul><ul><ul><li>The universe has a concrete age </li></ul></ul><ul><ul><li>Objects in the universe can change over time—older & more distant galaxies are different </li></ul></ul><ul><ul><li>Expansion resulted from an original explosion </li></ul></ul><ul><ul><li>Resembles biblical creation </li></ul></ul><ul><ul><li>Main proponent: Hubble </li></ul></ul><ul><li>Steady State </li></ul><ul><ul><li>The universe is eternal without beginning or end </li></ul></ul><ul><ul><li>The universe is ageless </li></ul></ul><ul><ul><li>Objects in the universe do not change over time—galaxies should appear the same regardless of distance or age </li></ul></ul><ul><ul><li>Expansion results from the creation of new matter </li></ul></ul><ul><ul><li>Resembles eastern religious beliefs found in Buddhism and Hinduism </li></ul></ul><ul><ul><li>Main proponent: Hoyle </li></ul></ul>
    29. 29. Big Bang Pioneers <ul><li>In 1927, the Belgian priest Georges Lemaître proposed that the universe began with the explosion of a primeval atom </li></ul><ul><li>Lemaître’s proposal came after astronomers discovered the redshifts of distant galaxies </li></ul><ul><li>In 1929, American astronomer Edwin Hubble found experimental evidence to support Lemaître's theory </li></ul><ul><li>Hubble matched his distance measurements of galaxies with redshift data to discover that distant galaxies in every direction are going away from us with speeds proportional to their distance </li></ul>http://en.wikipedia.org/wiki/Edwin_Hubble#Biography Lemaître & Hubble
    30. 30. Evidence for the Big Bang <ul><li>Expanding Universe </li></ul><ul><li>Galaxy evolution </li></ul><ul><li>Chemical elements in stars </li></ul><ul><li>Cosmic Background Radiation </li></ul><ul><li>Hydrogen and Helium </li></ul>
    31. 31. Expanding Universe <ul><li>Universe appears to be expanding due to the observation of redshifts in distant galaxies </li></ul><ul><li>This implies that the entire universe was together at one time and then exploded outward </li></ul>
    32. 32. Expanding Universe: Redshifts The farther away a galaxy is, the greater that its absorption lines are shifted towards the red-end of the spectrum
    33. 33. Redshift Note that the entire pattern of spectral lines is shifted to the right with the distant supercluster
    34. 34. Changing Galaxies (Galactic Evolution) <ul><li>Galaxies in the original Hubble Deep Field, the deepest image of distant galaxies, appear different than closer galaxies </li></ul><ul><li>This indicates that the galaxies have evolved over time </li></ul><ul><li>In a steady state universe, galaxies should look the same at any age or distance from earth </li></ul>
    35. 35. Hubble Deep Field (1996) <ul><li>The Hubble Deep Field is a 10-day long exposure of a tiny, apparently blank portion of the sky 1/30 of the full moon’s diameter </li></ul><ul><li>Released in 1996, the Deep Field represented views of the most distant galaxies yet obtained </li></ul><ul><li>Click: Hubble Ultra Deep Field </li></ul>http://hubblesite.org/newscenter/archive/releases/1996/01/image/a/
    36. 36. Creation of Elements <ul><li>The oldest known stars consist of mainly hydrogen and helium and lack heavier elements </li></ul><ul><li>New stars contain heavy elements recycled from older generations of stars that died and ejected their contents into space during supernova explosions </li></ul><ul><li>In a steady state universe, all stars would display similar amounts of chemical elements </li></ul>
    37. 37. Cosmic Background Radiation <ul><li>In 1965, Penzias and Wilson detected microwave radiation coming equally from all directions in space, day and night, all year. They later won the Nobel Prize for this discovery </li></ul><ul><li>This radiation indicates that space is filled with a slight amount of heat equal to 2.7 K </li></ul><ul><li>This heat is apparently the leftover fireball radiation of the Big Bang itself. The energy is extremely redshifted into the microwave region of the electromagnetic spectrum due to the universal expansion </li></ul><ul><li>In 1989, the Cosmic Background Explorer (COBE) satellite returned images of the cosmic background. </li></ul>http://bustard.phys.nd.edu/Phys171/lectures/cmbr.0.html
    38. 38. Cosmic Background (COBE) http://users.telenet.be/kosmonet/ruimtevaart/cobe.jpg
    39. 39. Cosmic Background (WMAP) The Microwave Sky The detailed, all-sky picture of the infant universe from three years of WMAP data. The image reveals 13.7 billion year old temperature fluctuations (shown as color differences) that correspond to the seeds that grew to become the galaxies. http://map.gsfc.nasa.gov/m_or.html
    40. 40. Hydrogen and Helium <ul><li>Most stars and galaxies contain from 25-28% helium </li></ul><ul><li>Stars produce helium from hydrogen during nuclear fusion reactions </li></ul><ul><li>Yet the amount of helium in stars is greater than would be produce in this manner </li></ul><ul><li>The majority of helium in stars was likely present from the start and was created during the Big Bang itself </li></ul><ul><li>Just after the Big Bang, the universe was temporarily hot enough to fuse hydrogen into helium which explains the extra helium in stars </li></ul>
    41. 41. What is the Universe Made of? <ul><li>Regular matter-5% (chemical elements) </li></ul><ul><li>Dark matter-25% </li></ul><ul><li>Dark energy-70% </li></ul>
    42. 42. Age of the Universe <ul><li>Original estimates were based on the Bible </li></ul><ul><li>For example, using Biblical chronology, Bishop Ussher dated the creation at October 23, 4004 BC </li></ul><ul><li>Modern estimates based upon WMAP observation of the CBR </li></ul><ul><li>Currently accepted age = 13.7 b.y. </li></ul>
    43. 43. Edge of the Universe <ul><li>Estimates of the radius of the universe are equal to the speed of light (c) divided by the Hubble Constant, c/H </li></ul><ul><li>This would equal the distance to the edge of the observable universe, the Hubble Radius </li></ul><ul><li>The edge of the universe is the Big Bang itself, this is as far back as we could ever look </li></ul>
    44. 44. Observable Universe The Hubble Radius today is about 13.7 billion light-years away in all directions. Inset: This HST Deep Field Telescope image shows some of the most distant galaxies we have seen.
    45. 45. Slice of Universe? This shows the slice of the universe surveyed by the 2dF Galaxy Redshift Survey. Every dot is a galaxy, with the Milky Way at the centre; distance from the centre is redshift and angle around the circumference is angle on the sky. There are 221,283 galaxies in this slice, which shows the highly-structured nature of the galaxy distribution. http://msowww.anu.edu.au/news/archive/2003/03_mar/
    46. 46. Olber’s Paradox <ul><li>Proposed by Heinrich Olbers in the 1800s, it questions why the sky is dark at night? </li></ul><ul><li>In an infinite universe, the sky wouldn’t be dark at night </li></ul><ul><li>The sky would be as bright as the surface of a star because every line of sight outward would eventually come to the surface of a star </li></ul>
    47. 47. Paradox Solved? <ul><li>With the Big Bang, the universe is not infinite, it had a definite origin in the distant past </li></ul><ul><li>Light from more distant stars had not had time to reach us yet, and the expansion of the universe will prevent this from ever happening </li></ul>In an infinite universe, every line of sight from earth would encounter a star—the sky should be bright at night, as bright as a star’s surface
    48. 48. Big Bang Image <ul><li>Just released-2008: Scientists have revealed image showing earliest moments of infant universe (next slide)… </li></ul>