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THE DARK UNIVERSE

THE DARK UNIVERSE. The Copernican Revolution continues… Caty Pilachowski, Mini-University 2010. DARK MATTERS. “Extraordinary claims require extraordinary evidence.” (Carl Sagan) “Extraordinary claims require extraordinary proof.” ( Marcello Truzzi )

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THE DARK UNIVERSE

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  1. THE DARK UNIVERSE The Copernican Revolution continues… Caty Pilachowski, Mini-University 2010

  2. DARK MATTERS • “Extraordinary claims require extraordinary evidence.” (Carl Sagan) • “Extraordinary claims require extraordinary proof.” (Marcello Truzzi) • “The weight of evidence for an extraordinary claim must be proportioned to its strangeness” (Laplace) • “A wise man, therefore, proportions his belief to the evidence” (David Hume)

  3. Journey into the Dark Universe • Foundation Concepts • Key Observations • Explaining Our Universe • Concordance Model • History of the Universe

  4. The Universe We See: Earth and Moon • Physical Sizes • Earth’s Diameter: 13000 km • Moon’s Diameter: ¼ Earth’s Diameter • Moon’s Distance: 400,000 km • Distance from Sun: 150,000,000 km • 8 light minutes

  5. The Universe We See: The Sun Physical Size Diameter: 1,400,000 km (about 100 x the diameter of Earth) Distance: about 100 x the Sun’s diameter

  6. The Universe We See:The Nearest Stars The closest star to our Sun is Proxima Centauri, about 4 light years distant (that’s about 40 trillion km)

  7. The Universe We See: The Milky Way Galaxy 100,000 LY The Sun is about 26,000 light years from the center Our Milky Way galaxy contains two hundred billion stars

  8. The Universe We See: The Local Galaxy Group Our Milky Way Galaxy is part of a cluster of about 3 dozen galaxies Andromeda is 3 million LY distant

  9. The Universe We See: The Local Supercluster Virgo Supercluster Our Local Group of galaxies is part of a larger Supercluster of galaxy groups Virgo is 60M LY distant

  10. Galaxies and clusters of galaxies collect into vast streams, sheets, and walls of galaxies. The Universe We See

  11. The Visible UniverseOn the largest scales, the universe seems to be more or less uniform

  12. The Universe we see is made of hydrogen and helium everything else 90% hydrogen atoms Helium 10% helium atoms Less than 1% everything else (and everything else is made in stars!) Hydrogen

  13. The Universe we see far away appears younger than the Universe nearby “Lookback time” Astronomers can see into the past

  14. THE DARKUNIVERSE • Missing Mass • Expansion • Acceleration • Foundation Concepts • Key Observations • Explaining our Universe • Concordance Model • History of the Universe

  15. The Case of the Missing Mass • In the 1930s, astronomer Fritz Zwicky noticed that galaxies in clusters were moving at speeds to fast to hold the cluster together • In the 1950s, astronomer Vera Rubin found that galaxies were spinning too fast to hold together Galaxies and galaxy clusters both behave as if more mass is present than we can see…

  16. Galaxy Rotation Mass within Sun’s orbit: ~1011MSun Total mass: ~1012MSun

  17. What’s the PROBLEM??? • The orbits of stars suggest that galaxies contain several times more mass that we can find in stars, gas and dust MISSING MASS! • Dark matteris the material believed to account for the discrepancy between the mass of a galaxy as found from the orbits of stars and the mass observed in the form of gas and dust

  18. The visible portion of a galaxy lies deep in the heart of a large halo of dark matter

  19. Evidence for Dark Matter Velocities of galaxies in clusters Rotation of galaxies Hot gas in galaxy clusters Velocities of stars in dwarf galaxies Galaxy interactions Collisions of galaxy clusters Gravitational lensing

  20. Velocity Dispersions in Dwarf Galaxies • Count the stars • Add up the light • Look for any gas • Add up the mass

  21. astro-ph/0704126 Calculated for a sample of 194 stars with 32-33 stars per bin Velocity Dispersions in Dwarf Galaxies • From spectra and the Doppler shift • Measure the velocity dispersion • Determine the total mass

  22. M/L Ratios for MW Dwarfs

  23. Galaxy interactions require more mass than we can see Antennae Galaxy (HST) Computer simulation The real thing

  24. Evidence for dark matter in clusters of galaxies We can measure the velocities of galaxies in a cluster from their Doppler shifts The mass we find from galaxy motions in a cluster is about 50 times larger than the mass in stars!

  25. Coma Cluster of Galaxies Visible Light X-Ray Light • HOT GAS IN GALAXY CLUSTERS • Clusters contain X-ray emitting hot gas • Temperature of hot gas tells us cluster mass • 7 x more gas than stars, but not enough!

  26. Gravitational Lensing • Light from a distant galaxy bends around a massive object (such as cluster of galaxies) between the distant galaxy and the observer • Gravitational lensing is predicted by Einstein's theory of general relativity

  27. Gravity bends the paths of light rays Gravity curves space, so mass acts as a lens The paths of all objects, whether or not they have mass, are curved if they pass near a massive body Prediction confirmed in the 1919 solar eclipse General Relativity

  28. Mysterious arcs discovered in 1986 Cluster Abell 370 (left) Cluster C12244 (right) The clusters and the arcs are at very different distances The arcs are highly distorted, very distant galaxies Discovering Gravitational Lenses

  29. Gravitational Lenses Produce Multiple Images source and lens aligned source and lens not aligned • If the source, the lens, and the observer lie in a straight line, the source will appear as a ring around the lens • If the lens is off-center, multiple, distorted images will be seen

  30. Cluster of Galaxies Cl0024+16 • The reddish objects are galaxies in the lensing cluster • The bluish objects are multiple images of a much more distant galaxy • Reconstruct the distant galaxy from individual pieces of the arc

  31. Arcs let us map the distribution of dark matter in clusters of galaxies

  32. cluster center The Bottom Line… • The visible matter does not provide enough gravity to produce the gravitational lenses we see from galaxies and galaxy clusters • Dark matter must be present to account for what we observe

  33. A cluster of galaxies consists of three components 1. 2% Stars 2. 13% Hot Gas 3. 85% Dark Matter The galaxies we see are only 2% of the mass

  34. 1E 0657-56 – The Bullet Cluster Direct observation of Dark Matter

  35. What’s going on with Cluster 1E 0657-56? • TWO clusters of galaxies collide

  36. The gas interacts, the dark matter and galaxies don’t The galaxies and dark matter pass through unimpeded, but the hot gas is separated from the clusters

  37. False Color: Blue = DM Red= Hot Gas White = Galaxies The Bullet Cluster Direct observation of Dark Matter

  38. All methods of measuring cluster mass indicate similar amounts of dark matter

  39. Clusters of Galaxies Gravity holds clusters together Coma Centaurus Gotta have Dark Matter! Perseus Hercules

  40. Dark Matter makes galaxies grow • Small galaxies form first, grow, and merge to form larger galaxies • The two objects approaching at the end will merge in about a billion years • Many of the small galaxies become satellites orbiting larger galaxies Galaxy formation is dominated by the gravitational pull of dark matter 4.3 Mpc or 14 million LY

  41. Galaxies Grow through Mergers Intergalactic gas Galaxy building blocks observed with Hubble Clumps concentrated by dark matter lead to galaxies Simulation The real thing The cosmic web of dark matter, gas, and galaxies in a young universe

  42. Dark Matter • The universe contains matter we cannot see • Dark matter interacts with normal matter through gravity • Dark matter does NOT interact with light the way the normal matter does • The Universe contains 5 or 6 times MORE dark matter than normal matter • All galaxies are embedded in clouds of dark matter

  43. What is DARK MATTER? • Can’t see it, taste it, touch it, smell it… • We can only detect it by gravity • We don’t know! Detecting Dark Matter is one of the most active areas of high energy physics, and a reason to build large accelerators.

  44. So, What Could It Be? • Dark Matter Candidates: • Black holes • Low-mass objects like loose planets • Elementary particles

  45. What about WIMPS?? • “Weakly Interacting Massive Particles” • As yet undiscovered elementary particles • High energy particle theories suggest such elementary particles exist  WIMPS are a plausible, but not firm, consequence of several theories in particle physics

  46. What about Dark Energy? First, the expansion of the Universe! Slipher*, Hubble, and Einstein *V. M. Slipher is an IU alumnus!

  47. Hubble found that the spectra of more distant galaxies are shifted toward the red – the further the galaxy, the larger the shift

  48. Hubble’s Law More distant galaxies are moving away from us at greater speed THE UNIVERSE IS EXPANDING

  49. Will the Universe Keep Expanding Or Re-Collapse???? • It depends on the density of the Universe • The critical density in the current epoch is 10-29 g/cm3, about one hydrogen atom per cubic meter • About 25 times more than the observed mass of stars and gas • Will dark matter recollapse the Universe? • There isn’t nearly enough to re-collapse the Universe But the universe isn’t even slowing down….

  50. The more we learn, the stranger it gets… • The speed of a ball tossed up in the air slows down because of gravity • Observations at the end of the 20th century established that the Universe is not just coasting, or slowing down because of its own gravitational pull, but actually speeding up.

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