The Cosmic Dawn's last glimmers

Scientists study dying light from most ancient of stars.


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 try to 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 NASA Goddard Space Flight Center in Greenbelt.

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 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."

Similarly, another team of scientists announced findings last week by using technology that allows astronomers to peer beyond what can they can actually see with the best equipment.

A team led by Zhi-Qiang Shen of the Shanghai Astronomical Observatory in China, using a network of radio telescopes, said that an energy source at the center of the Milky Way, believed to be a black hole, apparently does not take up as much space as previously thought.

The results show the object near the center of our Milky Way galaxy is smaller than the distance between the Earth and sun. Prior measurements suggested that it may have occupied a patch of space as wide as the solar system. The findings were also published in Nature.

The journal article was accompanied by a commentary by Christopher Reynolds, an astronomer at the University of Maryland College Park, who noted astronomers are on a path to probe "the structure and properties of some of the most enigmatic objects in the universe."

"It's a basic, fundamental desire and a need to discover where we came from, how we got here and how everything around us got here. Who knows what the implications are of what we discover," said Reynolds in an interview.

Short-lived 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, at astronomer at the California Institute of Technology.

One sure bet is that the early universe was a very different place than the one we live in. There were no black holes - the stars that formed them came much later. There also were no galaxies and stars like our sun, which is believed to have formed during a peak period of star production, 4 billion to 5 billion years ago.

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.

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