Oldest star in the universe spotted

28 Oct 2009

The most distant object yet spied in the universe is the remnant of a star about 13 billion light-years from Earth that sheds new light on the earliest days of the universe.

Two different teams of astronomers studied a brief but powerful flash of light, called a gamma-ray burst, from the star explosion.

Because of the time it takes for light to travel such distances, scientists think the exploded star must have been born about 600 million years after the big bang, when the universe was just 4 percent of its current age.

This means that the gamma-ray burst offers an unprecedented peek into a mysterious period known as the cosmic dark ages, which lasted from shortly after the big bang until about 900 to 800 million years ago.

Astronomers think the first stars started forming during the dark ages. But few such stars have ever been spotted, because the early universe was fogged with hydrogen gas that shrouded the starlight.

“Our group, and many others worldwide, have been working for years to catch such a rare event,” said Ruben Salvaterra of Italy’s Brera Astronomical Observatory, who was lead author on one of the studies.

The discovery gives researchers hope of spotting still older objects, including the first generation of stars that ever formed.

“Gamma-ray bursts are the most luminous phenomena in the universe,” said Dale Frail, whose team tracked radio emissions from the dying star using the National Radio Astronomy Observatory in Socorro, New Mexico. (See pictures of a gamma-ray burst that was visible from Earth to the naked eye.)

“This means that a bright gamma-ray burst could be detected out to the earliest times in the age of the universe.”

Text Message From Space

The newfound gamma-ray burst, dubbed GRB 090423, was first picked up in April by sensors aboard a NASA satellite called Swift.

The probe instantly swiveled its mirrors to monitor the burst, and soon after astronomers worldwide received alerts.

“We got text messages on our mobile phones, and we knew we had to jump into action,” said Nial Tanvir, an astronomer at the U.K.’s University of Leicester and lead author of the other optical study.

Different teams of astronomers using telescopes in Hawaii, New Mexico, Chile, and Spain all tracked the massive explosion as it faded away.

Salvaterra and Tanvir’s teams published their findings in two separate papers appearing this week in the journal Nature. Frail and colleagues posted their report last week to the Cornell University Web site Arxiv.org.

Breaking Up the Mist

Because of its extreme distance, the newfound gamma-ray burst shows that the star exploded before the dark ages ended thanks to reionization.

During the dark ages, the hydrogen atoms that permeated the universe were uncharged, so the gas blocked much of the radiation that we perceive as starlight.

But over time, light from the first stars ionized the hydrogen, turning it into a charged gas.

When this happened, “the universe went fairly rapidly from being opaque to suddenly being transparent,” Tanvir said. “It’s like on a foggy day, when the sun comes out and breaks up the mist.”

Gamma-ray bursts can shine through the haze of the dark ages, however, since a gamma ray is the most intense type of light known.

By studying more gamma-ray bursts, researchers might be able to figure out when the very first stars appeared and when they began to clear up the fog.

Bing Zhang, of the University of Nevada in Las Vegas, wrote a commentary also appearing in Nature but was not involved in any of the studies.

“The discovery,” Zhang wrote, “opens up the exciting possibility of studying the reionization epoch and the preceding cosmic dark ages.”

© 1996-2009 National Geographic Society. All rights reserved.


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