Brane Theory - Dark Matter and Parallel Worlds

Discussion in 'Politics' started by aphexcoil, Jan 3, 2004.


  2. Megan Watzke
    Chandra X-ray Observatory Center, CFA, Cambridge, MA
    Phone: 617-496-7998

    Science Contacts:
    David Buote, (949) 824-6280,

    RELEASE: 02-10

    Dark Matter Reality Check: Chandra Casts Cloud On Alternative

    New evidence from NASA's Chandra X-ray Observatory challenges
    an alternative theory of gravity that eliminates the need for
    dark matter. The observation also narrows the field for
    competing forms of dark matter, the elusive material thought
    to be the dominant form of matter in the universe.

    An observation of the galaxy NGC 720 shows it is enveloped
    in a slightly flattened, or ellipsoidal cloud of hot gas
    that has an orientation different from that of the optical
    image of the galaxy. The flattening is too large to be
    explained by theories in which stars and gas are assumed
    to contain most of the mass in the galaxy.

    "The shape and orientation of the hot gas cloud require it
    to be confined by an egg-shaped dark matter halo," said
    David Buote of the University of California, Irvine, and
    lead author of a report on this research in the 2002
    September 20 issue of The Astrophysical Journal. "This
    means that dark matter is not just an illusion due to a
    shortcoming of the standard theory of gravity -- it is

    According to the generally accepted standard theory of
    gravity, the hot X-ray cloud would need an additional
    source of gravity -- a halo of dark matter -- to keep
    the hot gas from expanding away. The mass of dark matter
    required would be about five to ten times the mass of
    the stars in the galaxy. If the dark matter tracked
    the optical light from the stars in the galaxy, the hot
    X-ray cloud would be more round than it is. The
    flattened shape of the hot gas cloud requires a flattened
    dark matter halo.

    An alternative theory of gravity called MOND, for
    Modified Newtonian Dynamics, was proposed in 1983 by
    Mordecai Milgrom of the Weizmann Institute in Israel,
    and has remained viable over the years. MOND does away
    with the need for dark matter by modifying the theory
    where the acceleration produced by gravity is very small,
    such as the outskirts of galaxies. However, MOND cannot
    explain the observations of NGC 720. This is apparently
    the first dynamical evidence that has successfully
    distinguished dark matter from MOND.

    The researchers also found that the Chandra data fit
    predictions of the cold dark matter theories, according
    to which dark matter consists of slowly moving particles,
    which interact with each other and "normal" matter only
    through gravity. Other forms of dark matter, such as
    self-interacting dark matter, and cold molecular dark
    matter, are not consistent with the observation in that
    they require a dark matter halo that is too round or too
    flat, respectively.

    "Chandra's ability to precisely identify and locate the
    point-like sources contaminating the diffuse emission in
    the X-ray image was absolutely essential," said Buote.
    "Only then could we make accurate measurements of the
    shape and orientation of the X-ray image contours."

    The conclusion from the Chandra data that NGC 720
    possesses a dark matter halo assumes that the hot gas
    cloud has not been unduly disturbed by collisions or
    mergers with other galaxies in the last 100 million years.
    The lack of evidence of such activity indicates that this
    assumption is valid.

    Chandra observed NGC 720, which is about 80 million light
    years from Earth, for 11 hours with the Advanced CCD
    Imaging Spectrometer (ACIS). Other members of the team
    includes Tesla Jeltema and Claude Canizares of
    Massachusetts Institute of Technology (MIT) in Cambridge,
    and Gordon Garmire of Pennsylvania State University in
    University Park. Penn State and MIT developed the
    instrument for NASA.

    NASA's Marshall Space Flight Center in Huntsville, Ala.,
    manages the Chandra program, and TRW, Inc., Redondo Beach,
    Calif., is the prime contractor for the spacecraft. The
    Smithsonian's Chandra X-ray Center controls science and
    flight operations from Cambridge, Mass.

    Images associated with this release are available on the
    World Wide Web at:


    [NOTE: An image supporting this release is available at
    and ]
  3. nitro


    Intersting stuff...

    When I have the time, I have to read these articles.


  4. Ditto - great articles. I'm interested in any more you find...