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The Dawn of Light

2 November 2005 (All day)
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Seeing stars. Stars and galaxies in the constellation Draco, as seen in an infrared image from the Spitzer telescope (top). When these stars and galaxies are subtracted from the image (bottom), the remaining glow may be from the first stars.

Astronomers have detected the collective glow from the universe's first stars, providing the first direct observation of a class of stars that hasn't existed for billions of years.

The earliest generation of stars, called population III, formed a few hundred million years after the big bang out of gas that was essentially only hydrogen and helium. Simulations have shown that the lack of heavier elements such as carbon and oxygen required these first stars to be huge--more than 100 times the mass of our sun. Such behemoths would have burned brighter than 10,000 typical modern stars, but only for a few million years. When they died, their ashes seeded the next generation of stars.

Now, astrophysicist Alexander Kashlinsky of Goddard Space Flight Center in Greenbelt, Maryland, and colleagues have found what they believe is a signature of these stars in infrared data from the Spitzer Space Telescope. The scientists analyzed the pattern of light in three small patches of sky, subtracting light from known stars and galaxies and accounting for dust in our own galaxy and solar system. Scattered throughout these patches, the astronomers found several bright spots, which appear to be imprints from the dawn of starlight, the authors conclude 3 November in Nature.

The bright clumps are not individual stars, which are too small to be seen, but regions of increased gas density. Just as tall mountains are more likely to be found in a mountain range, stars are more likely to be found in these denser places in space, Kashlinsky explains. However, these clumps could be confused with clusters of faint galaxies not detected by Spitzer, cautions astronomer Richard Ellis of the California Institute of Technology in Pasadena. Still, he believes the researchers make a reasonable argument that the spots are too bright to be anything but light from the first stars.

The fact that astronomers have not observed minigalaxies of population III stars in other surveys concerns Andrea Ferrara of SISSA/International School for Advanced Studies in Trieste, Italy. But Ellis notes that the first stars may have signed off well before galaxy formation--timing that will need to be confirmed by future observations.

Related sites
Alexander Kashlinsky's Web site
Spitzer Space Telescope
The Quest for Population III (a Science news story by Robert Irion)

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