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A1 23 The Universe
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Miller's Astronomy 1 lecture on The Universe

Miller's Astronomy 1 lecture on The Universe

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  • 1. Matter in the Universe LACC: §27.3, 27.4, 27.5 • Galaxy Distributions • Galaxy Cluster Distributions • Dark Matter An attempt to answer the “big questions”: What is out there? Thursday, May 20, 2010 1
  • 2. The Known Universe http://www.haydenplanetarium.org/universe Thursday, May 20, 2010 2
  • 3. Galaxy Distribution One of the candidates for "largest known structure in the Universe" is the "Sloan Great Wall", discovered in 2003 by J. Richard Gott III and Mario Juric and their colleagues, using SDSS data. The wall is nearly 1.5 billion light years in length and is located approximately one billion light years from Earth. The Sloan Great Wall is almost 3 times longer than the "Great Wall" of galaxies discovered in Margaret Geller and John Huchra's 1989 survey (which is also sometimes called the CfA2 Great Wall). At about 500 million light-years long, 300 million light-years wide and 15 million light-years thick, it was was previously the "record holder" for largest known structure. http://heasarc.gsfc.nasa.gov/docs/cosmic/sheets_voids_info.html Thursday, May 20, 2010 3
  • 4. Voids, Walls, and Filaments http://www.absoluteastronomy.com/topics/Large-scale_structure_of_the_cosmos Thursday, May 20, 2010 4
  • 5. Voids, Walls, and Filaments Stars are organized into galaxies, which in turn form clusters and superclusters that are separated by immense voids, creating a vast foam-like structure sometimes called the "cosmic web". Prior to 1989, it was commonly assumed that virialized galaxy clusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. However, based on redshift survey data, in1989 Margaret Geller and John Huchra discovered the "Great Wall," a sheet of galaxies more than 500 million light-years long and 200 million wide, but only 15 million light- years thick.... In April 2003, another large-scale structure was discovered, the Sloan Great Wall. One of the biggest voids in space is the Capricornus void, with an estimated diameter of 230 million light years. In August 2007, a possible supervoid was detected in the constellation Eridanus. It coincides with the 'WMAP Cold Spot', a cold region in the microwave sky that is highly improbable under the currently favored cosmological model. This supervoid could cause the cold spot, but to do so it would have to be improbably big, possibly a billion light-years across. In more recent studies the universe appears as a collection of giant bubble-like voids separated by sheets and filaments of galaxies, with the superclusters appearing as occasional relatively dense nodes. This network is clearly visible in the 2dF Galaxy Redshift Survey. In the figure a 3-D reconstruction of the inner parts of the survey is shown, revealing an impressive view on the cosmic structures in the nearby universe. Several superclusters stand out, such as the Sloan Great Wall, the largest structure in the universe known to date. http://www.absoluteastronomy.com/topics/Large-scale_structure_of_the_cosmos Thursday, May 20, 2010 5
  • 6. A Universe of Dark Matter This three- dimensional map offers a first look at the web-like large- scale distribution of dark matter, an invisible form of matter that accounts for most of the Universe’s mass http://www.youtube.com/watch? http://www.esa.int/esaSC/ v=gCgTJ6ID6ZA SEMZ6GSVYVE_index_0.html Thursday, May 20, 2010 6
  • 7. A Universe of Dark Matter Latest research In 2005, astronomers in the United Kingdom announced the discovery of the first dark galaxy, VIRGOHI21, lying 50 million light years away in the Virgo Cluster. Radio observations of the rotation of hydrogen gas in VIRGOHI21 have revealed there must be about a thousand times as much dark matter as hydrogen in this galaxy, and that its total mass is about one-tenth that of the Milky Way. http://www.daviddarling.info/encyclopedia/D/darkmat.html Thursday, May 20, 2010 7
  • 8. A Universe of Dark Matter Although the nature of dark matter remains uncertain, results published in February 2006 based on a study of 12 nearby dwarf galaxies have for the first time put numbers to some of its physical properties. This research shows that dark matter comes in "magic volumes", or standard packages, about 1,000 light-years (300 parsecs) across and containing about 30 million solar masses of material. Apparently, dark matter can't be crammed into spaces that are smaller than this. Another surprise is that the particles of which dark matter is made are moving on average with a speed of about 9 km/s, corresponding to a temperature of about 10,000 K – much higher than expected. This indicates that dark matter is neither hot nor cold but somewhere in between. In addition to dark matter, the universe contains large amounts of another invisible ingredient known as dark energy. Overall, the cosmos seems to consist of 4% ordinary matter (mostly in the form of hydrogen and helium), 23% dark matter, and 73% dark energy. http://www.daviddarling.info/encyclopedia/D/darkmat.html Thursday, May 20, 2010 8
  • 9. Matter in the Universe LACC: §27.3, 27.4, 27.5 • Galaxy Distributions: clusters and superclusters (clusters of clusters) • Galaxy Cluster Distributions: walls, voids and filaments • Dark Matter: seems to come in clumps of about 30 million solar mass, about 300 parsecs across, with a temperature of about 10,000 K An attempt to answer the “big questions”: What is out there? Thursday, May 20, 2010 9
  • 10. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 27, pp. 637: 8 Due at the beginning of next week’s first class period (unless there is a test that week, in which case it’s due the same period as the test). Thursday, May 20, 2010 10
  • 11. Properties of Our Universe LACC: §27.3, 27.4, 27.5 • The Cosmological Principle • The Shape of the Universe • The Size of the Universe An attempt to answer the “big questions”: What is out there? Thursday, May 20, 2010 11
  • 12. The Cosmological Principle The cosmological principle is a Copernican idea. It means we are not in a special place. On size scales of billions of light years, the universe is assumed to be uniform.... The discovery of the long superclusters may seem to endanger this assumption. On large enough scales though, the universe has many superclusters in all directions.... The idea of a uniform universe is called the cosmological principle. There are two aspects of the cosmological principle: • The universe is homogeneous. This means there is no preferred observing position in the universe. • The universe is also isotropic. This means you see no difference in the structure of the universe as you look in different directions. http://www.astronomynotes.com/cosmolgy/s3.htm Thursday, May 20, 2010 12
  • 13. The Cosmological Principle Isotropy means there are no special directions to the Universe, homogeneous means there are no special places in the Universe. http://abyss.uoregon.edu/~js/cosmo/lectures/lec05.html Thursday, May 20, 2010 13
  • 14. The Cosmological Principle ...for 100 Mpc regions the Universe is smooth to within several percent. Redshift surveys of very large regions confirm this tendency toward smoothness on the largest scales, even though nearby galaxies show large inhomogeneities like the Virgo Cluster and the supergalactic plane. http://www.astro.ucla.edu/~wright/cosmo_01.htm Thursday, May 20, 2010 14
  • 15. The Shape of the Universe http://www.youtube.com/watch?v=3WL_vtu4r1w 4:36 Thursday, May 20, 2010 15
  • 16. Shape of the Universe Three-dimensional curved space is not possible to visualize, but curvature in two dimensions can be illustrated. A positively curved universe is like the surface of a sphere; a negatively curved universe, like a saddle. A universe with zero curvature is like a plane. The geometry of curved space, two- or three-dimensional, is different: parallel lines may intersect (positively curved space) or may diverge (negatively curved space) and the sum of angles in a triangle may be more than 180 degrees (positively http://www.nap.edu/openbook.php? curved space) or less than 180 record_id=10079&page=82 degrees (negatively curved space). Thursday, May 20, 2010 16
  • 17. Shape of the Universe "Closed," "open," and "flat" actually refer to the shape, or curvature, of space-time itself. Impossible to picture in three spatial dimensions, this is easy enough in two: • Two-dimensional space with positive curvature would resemble the surface of a sphere (on which parallel lines converge). • Two-dimensional space with negative curvature would be like the surface of a saddle or a Pringle's potato chip (on which parallel lines diverge). • A flat two-dimensional universe would resemble a sheet of paper (on which parallel lines stay parallel). Many independent observations indicate that the universe is in fact flat. http://www.lbl.gov/Science-Articles/Archive/SNAP-3.html Thursday, May 20, 2010 17
  • 18. Size of the Universe Imagine the universe just a million years after it was born, Cornish suggests. A batch of light travels for a year, covering one light-year. "At that time, the universe was about 1,000 times smaller than it is today," he said. "Thus, that one light-year has now stretched to become 1,000 light-years." All the pieces add up to 78 billion-light- years. The light has not traveled that far, but "the starting point of a photon reaching us today after traveling for 13.7 billion years is now 78 billion light- years away," Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger. http://www.space.com/scienceastronomy/mystery_monday_040524.html Thursday, May 20, 2010 18
  • 19. Properties of Our Universe LACC: §27.3, 27.4, 27.5 • The Cosmological Principle--our universe is homogeneous (looks the same no matter where you are) and isotropic (looks the same in all directions) • The Shape of the Universe: open (negatively curved), closed (positively curved), or flat (zero curvature); our universe seems remarkabley flat • The Size of the Universe: light from an object that appears 13 billion lightyears away is now probably about 75 billion lightyears away An attempt to answer the “big questions”: What is out there? Thursday, May 20, 2010 19
  • 20. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 27, pp. 637: 11 (for #11, I just need yes-or-no answers). • Ch 28: Tutorial Quizzes accessible from: http:// www.brookscole.com/cgi-brookscole/course_products_bc.pl? fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of next week’s first class period (unless there is a test that week, in which case it’s due the same period as the test). Thursday, May 20, 2010 20