[Paleopsych] NYT: Making the Universe a Little Closer and Brighter

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Science > Space & Cosmos > Making the Universe a
Little Closer and Brighter
http://www.nytimes.com/2005/04/26/science/space/26lens.html

    By DENNIS OVERBYE

    In a kind of belated birthday present to Albert Einstein, whose
    theory of relativity is 100 years old this year, astronomers say they
    have confirmed an essential but previously unconfirmed prediction of
    general relativity, namely that the entire universe can act as a
    magnifying lens.

    The light from distant quasars, enigmatic and violent galaxy-birthing
    events on the shores of time, some 10 billion light-years away, has
    been magnified by the gravitational force of lumps and irregularities
    in the structure of the nearby cosmos. So the quasars appear slightly
    brighter in telescopes than they actually are, according to a
    multinational team of researchers led by Dr. Ryan Scranton of the
    University of Pittsburgh.

    They reached that conclusion after sifting a mountain of data about 13
    million galaxies and other celestial objects, obtained by the Sloan
    Digital Sky Survey, a continuing effort to remap the heavens.

    The magnification, they said, confirms the dark picture cosmologists
    have built up in the last few years, in which the atoms that make up
    stars and people are overwhelmed by clouds of mysterious dark matter
    and that matter is in turn overwhelmed by something even stranger,
    so-called dark energy, which seems to be wrenching space and time
    apart faster and faster, taking the galaxies for a potentially fatal
    ride into endless cold and loneliness.

    "This is all hanging together," said Dr. Scranton, lead author of a
    paper that will be published in The Astrophysical Journal and is being
    posted today on the physics Web site, [1]www.arXiv.org. The
    astronomers said that cosmic magnification gave them a new way to
    weigh the universe and to investigate its evolution.

    Dr. Robert Nichol, a member of the team from the University of
    Portsmouth in England, said, "In this year of Einstein, it is a
    wonderful demonstration of the power of general relativity as it shows
    that light travels to us on a very 'bumpy road' from these quasars."

    Dr. Tony Tyson, a gravitational lensing expert at the University of
    California, Davis, said: "It is nice to close the loop on Einstein
    here. This all traces back to Einstein's prediction of light bending."

    Einstein's theory, promulgated in 1915, and spectacularly supported by
    observations during a solar eclipse in 1919, ascribes the effect we
    call gravity to the warping of space-time geometry by matter or
    energy. As one consequence, the theory says, lumps of mass, like a
    star, a galaxy or a whole cluster of galaxies with their attendant
    clouds of dark matter, can act as a gravitational lens, magnifying
    very distant objects.

    In recent decades astronomers have recorded instances in which the
    images of galaxies or quasars have been distorted into arcs or rings
    or even split into multiple images by the gravity of intervening
    galaxies, so-called gravitational lenses. And they have seen
    individual stars appear to flare as their light is magnified by the
    gravity of a passing star.

    Astronomers have observed a distortion in the shapes of distant
    background galaxies, known as cosmic shear, because of the large-scale
    structure of the universe, but until now they have not been able to
    make a reliable measurement of the cosmic magnification factor.

    Now, in the Sloan survey, said Dr. Nichol, "we see the summed
    magnification of all quasars by the intervening masses in the
    universe." He estimated that mass, the contents of the universe out to
    about 2.5 billion light-years, as roughly equivalent to 100 billion
    billion Suns.

    "This is a measurement that's been hanging around in the background,"
    said Dr. Scranton, who added that earlier attempts at the measurement
    had resulted in "a huge mess" because data about the heavens lacked
    the needed precision. The results, he said, did not match the standard
    cosmological theory or one another.

    The present calculation was based on a sample of 13 million galaxies
    and 200,000 quasars derived from the mammoth Sloan survey. Begun in
    1998 with a custom built telescope at Apache Point Observatory in New
    Mexico, the survey was created to measure the colors and brightnesses
    of several hundred million objects over a quarter of the sky and map
    the distances to a million galaxies and quasars.

    "We have the biggest set of quasars ever assembled," Dr. Scranton
    said. The quasars, thought to be black hole fireworks in young
    galaxies, are all out about 10 billion light-years away, their light
    has been on the way to us since the universe was 4 billion years old.

    The Sloan galaxies are in front of them, roughly 2.5 billion
    light-years away.

    Because quasars are wildly erratic and far, far away, there is no way
    to tell by how much any one of them has been magnified. As a result
    astronomers resorted to statistical methods, looking for correlations
    between the numbers of quasars and the locations of galaxies on the
    sky.

    Quasars too faint to show up normally should pop into view near
    galaxies that have amplified the quasars' light, swelling the counts.
    But, as Dr. Scranton explained, there is a competing effect at work.
    The bending of light rays by those same galaxies will also cause the
    quasars to appear to be displaced outward slightly from the galaxy
    lowering their apparent density on the sky.

    The two effects can only be separated and the magnification confirmed
    after the quasars and galaxies have been sifted and resifted according
    to their colors and apparent brightnesses by powerful computer codes.

    The detection of the magnification is a triumph of computer science as
    well as astronomy, the astronomers say.

    Because both dark and visible matter contribute to gravity and thus to
    the cosmic magnification, Dr. Scranton said, astronomers can use the
    effect to investigate the dark side of the universe, looking into
    questions like how galaxies form and whether galaxies and dark matter
    coincide.

    So far, he said, "The galaxies basically trace the dark matter very
    clearly."

    He added, "It would be nice if it were more exotic, but its pretty
    much another brick in the structure," he added, referring to the
    so-called concordance cosmology of dark matter and dark energy.

    Dr. Max Tegmark, a cosmologist at the Massachusetts Institute of
    Technology, called the detection of cosmic magnification "a big deal,"
    and said, "I think it will emerge as a powerful cosmological tool."

    Dr. Tyson, however, said he doubted that cosmic magnification would
    emerge as an important cosmological tool. It might be easier, he said,
    to get information from cosmic shear, the distortion of distant
    galaxies, noting that there are many more of those than of quasars.
    Dr. Tyson heads a group that is planning to build a large telescope
    and camera, known as the Large Synoptic Survey telescope, to do just
    that.

    But, he added, referring to the prospects for cosmic magnification, "I
    would be very pleased to eat my hat on that one." The Sloan survey, he
    said, shows what you can do with a large well-controlled astronomical
    survey.

    "The sky's the limit," he said.

References

    1. http://www.arXiv.org/