First Stars in Universe Detected?

Brian Handwerk
for National Geographic News
November 2, 2005
NASA researchers say they have detected what may be the faint infrared glow of the first stars in the universe.

Known as population III stars, the distant bodies are thought to have formed just 200 million years after the big bang, the event that in theory created the universe some 14 billion years ago.

The original stars formed from gas and dust in the void of space and are thought to have been many times more massive than today's stars. The ancient stars remain invisible to telescopes and have never been detected before.

"They have basically been theoretical objects," said Alexander Kashlinsky, an astronomer at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Using NASA's orbiting Spitzer Space Telescope, Kashlinksy and his colleagues identified the stars indirectly by measuring the enduring energy that they once radiated into the void of space.

Cosmic Radiation

As the universe expands, starlight is stretched into longer, redder wavelengths. Most emissions from the first stars in the universe would appear today as infrared light.

The universe is filled with background radiation known as the cosmic infrared background (CIB). This includes radiation from all stars—young and old, near and far.

"If these [earliest stars] were very massive and formed in the standard cosmological mode, they should have left a signature in the fluctuations of the CIB. That's the signal we sought to measure with these observations," Kashlinsky said.

To detect the original stars, the team had to isolate their energy from that of countless other bodies, a task akin to picking out a group of voices amid cheering fans at a crowded sports stadium.

"Imagine a field filled with electric bulbs of varying intensity, from one watt to several hundred watts," Kashlinsky explained. "You look at this field, and you want to actually see the faintest bulbs."

"So you start removing bright bulbs that you can individually identify. Once you've done that, you can see an image of what the field is like and what it is filled with. From that, you can deduce a collective signal."

Using a similar process, Kashlinsky and his colleagues systematically ruled out the radiation contributed by stars and galaxies between Earth and the extremely distant population III stars.

The remaining radiation was larger than expected and fluctuated unevenly across the sky. Kashlinsky and colleagues believe that energy reflects the original stars.

But the cutting-edge observations are sure to raise new questions.

Richard Ellis, an astronomer at the California Institute of Technology in Pasadena, cautioned that the NASA team "had to remove all the foreground material to see the signal, so the natural suspicion is that they didn't do it correctly."

"I'm worried about having to remove all the light from all of the galaxies between us and these very first stars," he added. "They have a good model and they did a convincing job. But we don't know the history of galaxy formation with high precision."

The new study and a related commentary by Ellis appear in tomorrow's issue of the science journal Nature.

Birth of Starlight

The theoretical implications of detecting the first starlight could be far ranging.

"Soon after the big bang the universe was a dark place. Nothing was shining," Ellis said. "Astronomers are trying to determine what the physical conditions were when stars switched on for the first time."

There are different theories to explain the birth of starlight. A multitude of stars might have begun twinkling en masse over a relatively short period. Alternatively, stars might have switched on much more gradually.

The new findings may add some weight to the first theory.

"If [this research] is correct, it would suggest that it was a very brief period in history when the stars switched on," Ellis said. "If that's true, understanding what to look for and what period in time it happened is something that everybody would like to know."

NASA's Kashlinsky noted, "We might learn from such data, in the future, how bright the stars were, how many there were, and how matter was distributed."

The findings seem likely to spark further attempts to glimpse the first stars and grasp their importance.

"They've claimed to see something, and everybody will get excited. Some will believe and others won't. But it's a significant step forward in the subject," Ellis said. "It's a very important scientific question."

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