[Paleopsych] NYT: Stars on Diet: Weight Is Limited to 150 Suns, Researchers Find

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Science > Space & Cosmos > Stars on Diet: Weight
Is Limited to 150 Suns, Researchers Find
March 10, 2005


    WASHINGTON, March 9 - The universe is full of stars, but there appear
    to be few really fat ones. Astronomers said Wednesday that there
    seemed to be a stellar weight limit equivalent to 150 Suns, but no

    Using the Hubble Space Telescope to examine one of the densest
    clusters of stars in the Milky Way, which should have been brimming
    with fat stars, astronomers said they found a sharp cutoff in the mass
    of bodies that form in this stellar nursery.

    In examining hundreds of stars in the dense Arches cluster, Dr. Donald
    F. Figer and colleagues at the Space Telescope Science Institute in
    Baltimore said they could not find any larger than 130 solar masses,
    or equal to the mass of 130 of our Suns.

    "We are surprised at this result because we expected to find stars up
    to 500 to 1,000 times more massive than our Sun," Dr. Figer said.

    At a telephone news conference organized by the National Aeronautics
    and Space Administration, experts called the findings a step to
    understanding star formation.

    Dr. Sally Oey of the University of Michigan said that the findings,
    published in the March 10 issue of the journal Nature, were consistent
    with studies of smaller star clusters in our galaxy and observations
    she and colleagues had conducted of a huge star cluster in a galactic
    neighbor, the Large Magellanic Cloud.

    The denser a cluster, the better the chance of finding giant stars,
    Dr. Oey said.

    The Arches cluster that Dr. Figer examined, she said, "is the richest
    cluster in our galaxy." Because of this, astronomers said, it is
    highly unlikely that they would find superheavy stars elsewhere.

    Astronomers have been uncertain about how massive a star can grow
    before it cannot hold itself together and blows apart.

    Consequently, theories have predicted that stars can be 100 to 1,000
    times more massive than the Sun. It has been easier to predict a lower
    weight limit for stars, experts said, because objects less than
    one-tenth the mass of our Sun are not heavy enough to sustain nuclear
    fusion in their cores to shine.

    "These are fantastic findings," Dr. Stanford E. Woosley of the
    University of California, Santa Cruz, said of Dr. Figer's work.

    Giant stars, at more than 100 solar masses, are important to galaxies
    and the universe because their furious combustion produces many
    important elements to form planets and other bodies like carbon,
    oxygen, sodium and neon, Dr. Woosley said.

    The big stars also are short-lived, he said, with no star more than
    100 solar masses lasting more than three million years because they
    consume their fuel so rapidly.

    The Sun, by contrast, is 4.55 billion years old and expected to last 5
    billion more years before running out of fuel. In mass, the Sun is
    equal to 300,000 planets the size of the Earth.

    Dr. Figer said that although he found no star bigger than 130 solar
    masses in his observations, he set the upper limit for a big star at
    150 solar masses to be conservative.


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