Telescopes have witnessed a flash of light from the most distant single star ever seen. The blast, called a gamma ray burst (GRB), probably arose from the explosive death of a star when the universe was just 900 million years old. The event, described today at a NASA news briefing, should yield new insights into the types of stars that existed in the first galaxies.
Astronomers believe many GRBs mark the origins of black holes at the cores of giant stars that have consumed their nuclear fuel. As matter plunges toward a new black hole, it heats up so violently that jets of gamma rays rifle into space. Theorists have predicted that telescopes could see such events from a time just a few hundred million years after the big bang, near the margins of the visible universe. But to catch them, astronomers needed a NASA satellite called Swift--launched in November 2004 (ScienceNOW, 24 January 2005) to spot GRBs and transmit their positions to telescopes on the ground within seconds.
Swift worked perfectly on 4 September, spotting faint traces of a flare in the constellation Pisces. Astronomer Daniel Reichart of the University of North Carolina at Chapel Hill knew that the faintness might point to an extremely distant burst. Working via the internet, Reichart's team checked the site of the GRB with the 4.1-meter Southern Observatory for Astrophysical Research telescope atop Cerro Pachon, Chile. Within about 3 hours, the telescope saw a fading "afterglow" in infrared light--the heat of an expanding fireball of debris from the explosion.
Other observers worldwide have verified the find. Precise analysis of the afterglow's spectrum of light by the 8.2-meter Subaru Telescope atop Mauna Kea, Hawaii, pinpointed the GRB's extraordinary distance: 12.77 billion light-years from Earth, about 500 million light-years beyond the previous record-holder. The new burst erupted in the epoch when the first galaxies were coalescing.
"This burst opens the door to the use of GRBs as unique and powerful probes of the early universe," says astrophysicist Donald Lamb of the University of Chicago in Illinois. He expects Swift will pinpoint the time when the universe began to create huge stars by spotting even more distant GRBs, from the first 200 million to 500 million years of cosmic history. And by analyzing the light as it passes through clouds of gas and on its way to Earth, astronomers will glean the compositions of the earliest galaxies, Lamb adds.