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NASA telescope sees oldest starlight ever found

Astronomers say findings open window into 'big bang' theory

By studying traces of ancient starlight, astronomers are gaining a better understanding of how the infant universe took shape — a step toward answering questions about the nature of space, time and energy as defined by Einstein's theories.

But the deeper in space that scientists probe, the murkier things become. Even with ever-improving technology, the oldest stars are still too distant to observe directly. In probing this and other enigmatic phenomena, astronomers often make assumptions based on what the latest instruments reveal.

"We don't have the telescopes now to see these stars. They're small and very far away, so we look for signatures from the light that came from them," said Alexander Kashlinsky, a cosmologist at the National Aeronautics and Space Administration's Goddard Space Flight Center in Greenbelt, Md.

Studying these light signatures, Kashlinsky and a team of researchers, using NASA's Spitzer Space Telescope, announced last week that measurements of infrared light from a far corner of the sky turned up what they say is the most ancient starlight ever found. The findings were published in a recent issue of the journal Nature.

The researchers analyzed ripples in ancient cosmic radiation — light invisible to the human eye — by filtering out light from closer and more recently developed stars.

Kashlinsky said the search was like sorting out the dimmest light bulbs among a vast field of bright and dim bulbs. The ancient stars have long since burned out, but large groups of them have left infrared signatures, he said. "What we observed was the emissions from superclusters that are made up of these stars."

Astronomers say the findings on ancient starlight open a window into a universe created by a cosmic explosion, known as the "big bang," that hurled matter in all directions. Initially, the explosion produced hydrogen and helium, but the universe remained in a fog for up to a billion years, a mysterious stretch known as the Cosmic Dark Ages.

The elements that made life possible, such as carbon and oxygen, came much later with the intense heat and gravitational forces produced by stars.

Astronomers are still unsure about how and when the earliest stars formed — an event called the Cosmic Dawn.

They say the light came from stars that were hundreds of times larger, thousands of times brighter and with much shorter life spans than any stars seen today.

Many of the ancient stars were formed when the universe was a mere 100 million years old and burned out after 100 million years, scientists say.

By contrast, our sun is expected to have a life span of about 10 billion years.

"There are still unanswered questions about these early stars. Did they gradually switch on, or how suddenly did they appear in the sky?. We just don't know" said Richard Ellis, an at astronomer at the California Institute of Technology.

Scientists can determine the age of closer stars by measuring the types of light they emit. Younger stars produce more blue light and more gases created by burning off heavier elements. When viewing light from distant stars, we see light emitted millions or billions of years ago.

Astronomer Edwin Hubble found in 1929 that the universe is expanding, with galaxies flying away from each other. By tracing that expansion back in time, scientists estimated the age of the universe at 13.7 billion years.

Light waves arriving from the first stars and galaxies have traveled for so long that they have been literally stretched by the expansion of the universe, changing from visible to longer infrared wavelengths. The process, known as "redshift," is used to judge the age of light from very distant stars.

Kashlinsky's team used the Spitzer telescope, launched just two years ago, because it can pick up light in the infrared, allowing for views of distant stars.

But much of the light from the oldest stars is still too far away to study in detail, even with the most sophisticated probes and telescopes. Some astronomers wonder if others can make sound assumptions about ancient stars, like those described in the Nature study, that can't be directly observed.

"If these stars do exist, they'd be really faint, so faint, it's been difficult to see them," said Hsiao-Wen Chen, an astronomer at the University of Chicago. "Nobody's been successful yet."