WORLD SCIENCE

"Long before it's in the papers"
August 03, 2010

Nov. 2, 2005
Courtesy Spitzer Space Telescope
and World Science staff

The first stars in the universe are long gone, scientists say—but the light they emitted eons ago should still be reaching us, letting us see them. Astronomers now report having possibly detected their faint glimmer. 

If confirmed, they say the finding provides a glimpse of an era more than 13 billion years ago, when the universe came alive after millions of years of darkness following the explosion that created the cosmos. 

This artist's concept shows what the very early universe might have looked like, just after its first stars began bursting onto the scene. [NASA/JPL-Caltech/R. Hurt (SSC)]

The light could also be from hot gas falling into the first black holes, though, the scientists added. 

The research team, based at NASA Goddard Space Flight Center in Greenbelt, Md., described the observation as seeing the glow of a distant city at night from an airplane. The light is too distant and feeble to resolve individual objects. 

“We think we are seeing the collective light from millions of the first objects,” said Alexander Kashlinsky, lead author of a paper describing the findings that appeared in the Nov. 3 issue of the research journal Nature. “The objects disappeared eons ago, yet their light is still traveling across the universe.” 

The researchers used NASA’s Spitzer Space Telescope to make the find. The telescope is an orbiting observatory that sees infrared light, a type of light slightly less energetic than visible light.

Scientists theorize that space, time and matter originated about 13.7 billion years ago in the Big Bang, when everything exploded out of a single point. Another 200 million years would pass before the first starlight, according to the theory. 

A 10-hour observation by Spitzer in the constellation Draco captured a diffuse glow of infrared light, lower in energy than visible light and invisible to us, the researchers said. They added that this glow is likely from Population III stars, a hypothesized class of stars thought to have formed before all others. Population I and II stars, named by order of their discovery, comprise the familiar types of stars we see at night.

Theorists say the first stars were likely over a hundred times heavier than Earth’s sun and extremely hot, bright, and short-lived, each one burning for only a few million years. The light that Population III stars emitted would be “redshifted,” that is, their light rays would be stretched out. This is due to the fact that they were zooming away from our area of the universe, as a result of the continuing expansion of the cosmos.

Due to redshifting, the light from these objects should be detectable as infrared.

“This deep observation was filled with familiar-looking stars and galaxies,” said John Mather, a co-author of the paper. “We removed everything we knew—all the stars and galaxies both near and far. We were left with a picture of part of the sky with no stars or galaxies, but it still had this infrared glow with giant blobs that we think could be the glow from the very first stars.” 

“This difficult measurement pushes the instrument to performance limits that were not anticipated in its design,” said team member S. Harvey Moseley.

The camera’s high resolution enabled the team to remove the fog of foreground galaxies, made of later stellar populations, until the cumulative glow of the “first light” shone forth, the researchers said.

The team noted that future missions, such as NASA’s James Webb Space Telescope, will find the first individual clumps of these stars or the individual exploding stars that might have made the first black holes. 

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