A powerful gamma-ray burst (GRB) detected by NASA's Swift satellite in April – the most distant object ever discovered – continues to provide tantalizing insight into the nature of objects born in the early Universe.

“This observation allows us to begin exploring the last blank space on our map of the Universe,” says Professor Nial Tanvir of the University of Leicester.

GRB 090423 is located at a spectacularly distant 13 billion light years, emanating from a star that exploded when the Universe was just 630 million years old. Most GRBs occur as their progenitor stars run out of fuel and collapse into a black hole or neutron star, shooting out jets of radiation through previously expelled layers of gas, which interact to generate short-lived afterglows in other wavelengths.

“This explosion provides an unprecedented look at an era when the Universe was very young and also was undergoing drastic changes,” says Dale Frail of the National Radio Astronomy Observatory. “The primal cosmic darkness was being pierced by the light of the first stars and the first galaxies were beginning to form. The star that exploded in this event was a member of one of these earliest generations of stars.”

Astronomers using the Very Large Array (VLA) detected the first radio waves a week following the Swift detection, and recorded changes in the object until it faded from view more than two months later. Much of the light was in the form of very high energy gamma rays, fading into infrared wavelengths.

“It’s important to study these explosions with many kinds of telescopes,” says Derek Fox of Pennsylvania State University. “Our research team combined data from the VLA with data from X-ray and infrared telescopes to piece together some of the physical conditions of the blast. The result is a unique look into the very early Universe that we couldn’t have gotten any other way.”

The combined data collection efforts reveal that the explosion of the progenitor star was more energetic than other known GRBs, a near-spherical blast that expanded into a tenuous and relatively uniform gaseous medium surrounding the star. Astronomers suspect that the Universe's first inhabitants were brighter, hotter and more massive than those that formed later, and hope to build evidence for this theory in the shape of even more distant GRBs. While the data on GRB 090423 don’t indicate that it resulted from the death of such a monster star, new astronomical tools are coming that may reveal them.

“The Atacama Large Millimeter/submillimeter Array (ALMA), will allow us to pick out these very-distant GRBs more easily so we can target them for intense follow-up observations,” says Frail. “The Expanded Very Large Array, with much greater sensitivity than the current VLA, will let us follow these blasts much longer and learn much more about their energies and environments. We’ll be able to look back even further in time.”

Both ALMA and the EVLA are scheduled for completion in 2012.

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