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COSMOLOGY
Evidence Reported For Acoustic Oscillations In Early Universe

Throughout the Universe, galaxies tend to swarm in groups ranging from just a handful of members to casts of thousands. Astronomers have realized since the early 1970s that the larger swarms, immense clusters of galaxies millions of light-years across, are immersed within tenuous clouds of hot gas which glow strongly in x-rays. These clouds may have been heated by their collapse in the early Universe, but in many galaxy clusters, the gas appears to be cooling.

This Chandra Observatory x-ray image reveals a striking cooling flow in the central regions of the galaxy cluster cataloged as Abell 1795. Brighter pixels in the false-color image represent higher x-ray intensities. The bright filament down the center indicates gas condensing and cooling -- rapidly loosing energy by radiating x-rays. At the very top of the filament is a large, x-ray bright galaxy. As it moved through the cluster gas cloud, the massive galaxy's gravitational influence seems to have created this cosmic wake of denser, cooling gas. Continuing to cool, the cluster gas will ultimately provide raw material to form future generations of stars.

  • Image Credit: Abell 1795: A Galaxy Cluster's Cooling Flow A. Fabian (IoA Cambridge) et al., NASA. Caption Credit:  APOD.
  • Pittsburgh - May 24, 2001
    In findings reported in tomorrow's issue of the journal Science, Carnegie Mellon University and University of Maine astrophysicists say they have confirmed the existence of acoustic oscillations generated shortly after the explosive birth of the universe.

    The scientists say their evidence links the existence of acoustic oscillations, or wiggles, in the distribution of both the cosmic microwave background radiation and the distribution of matter throughout the universe.

    These acoustic "waves" were first found in the cosmic microwave background radiation (CMB), generated when the universe was a mere 300,000 years old.

    Now, with the discovery of these oscillations in the matter, scientists have a direct connection between the universe today and the universe as it was more than 10 billion years ago.

    "For decades, researchers have theorized that there should be acoustic oscillations in the cosmic background radiation, as well as the matter distribution of the universe," said Carnegie Mellon post-doctoral researcher Christopher Miller, lead author of the paper.

    "Finally, only a month ago, researchers discovered them in the CMB. Today, we have found these same oscillations in the matter.

    "Not only do these results provide support for the Hot Big Bang Inflationary Model, but they also show we understand the physics of the early universe. This physics can take us forward in time, predicting the matter-density distribution from the cosmic microwave background (CMB), or backward in time, predicting the CMB using the distribution of galaxies and clusters of our local universe."

    Miller, Carnegie Mellon Assistant Professor of Physics Robert Nichol and University of Maine Associate Professor of Physics David J. Batuski drew their data from three cosmological surveys: the Abell/ACO Cluster Redshift Survey; the IRAS Point Source redshift catalog and the Automated Plate Machine cluster catalog.

    Using the astrophysical data, the Carnegie Mellon team was able to take a "snapshot" of a part of the universe as it is and compare it to another "snapshot," or data set, from the universe as it was only 300,000 years after the Big Bang.

    "We have worked for several years determining the distribution of galaxy clusters in a large part of the universe," Batuski said. "It is satisfying to have information on such a large number of clusters and volume of space, that we can compare with the structure of the very early universe seen in the CMB."

    Last week, similar findings were reported by a team of scientists using a different set of data gathered from the Anglo-Australian Telescope.

    Confirmation of the acoustic oscillations means that the Big Bang theory has survived another major test. These measurements confirm that the universe was once hot, fluid-like plasma, in which scientists would expect to see acoustic "waves" in both the photons and matter that comprised the early universe.

    "Findings like these show we are starting to understand the general framework of the universe we live in," Nichol said. "In the next decade or two, with tens of times more data, we will continue to test the predictions of our Cosmological Standard Model and determine what is the dark matter and energy."

    "Now that we understand this framework, we can decouple the evolution of the universe from the evolution of galaxies and start attacking other fundamental questions like how did galaxies form and why? It's great to be a cosmologist!"

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    Hilo - May 20, 2001
    A team of astronomers from the National Astronomical Observatory of Japan, the University of Tokyo, and Kyoto University has completed a careful analysis of a very deep image taken at near-infrared wavelengths.



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