GRB 090423 Gamma-Ray Burst Smashes Cosmic Distance Record

April 29, 2009:

NASA's Swift satellite and an international team of astronomers have found a gamma-ray burst from a star that died when the universe was only 630 million years old--less than five percent of its present age. The event, dubbed GRB 090423, is the most distant cosmic explosion ever seen.

"The incredible distance to this burst exceeded our greatest expectations -- it was a true blast from the past," says Swift lead scientist Neil Gehrels at NASA's Goddard Space Flight Center.

GRB 090423 as seen by NASA's Swift satellite. The image is a composite of data from Swift's UV/Optical and X-Ray telescopes. Credit: NASA/Swift/Stefan Immler

The burst occurred at 3:55 a.m. EDT on April 23rd. Swift quickly pinpointed the explosion, allowing telescopes on Earth to target the burst before its afterglow faded away. Astronomers working in Chile and the Canary Islands independently measured the explosion's redshift. It was 8.2, smashing the previous record of 6.7 set by an explosion in September 2008. A redshift of 8.2 corresponds to a distance of 13.035 billion light years.

"We're seeing the demise of a star -- and probably the birth of a black hole -- in one of the universe's earliest stellar generations," says Derek Fox at Pennsylvania State University.

Gamma-ray bursts are the most luminous explosions in the Universe. Most occur when massive stars run out of nuclear fuel. As their cores collapse into a black hole or neutron star, jets of matter punch through the star and blast into space. There, they strike gas previously shed by the star and heat it, which generates short-lived afterglows in many wavelengths.

For years, astronomers have been hunting for gamma-ray bursts from the earliest generations of stars--and mysteriously failing to find them. The detection of GRB 090423 is an important milestone in the quest to locate bursts in the redshift range 10 to 20. More information: "The Case of the Missing Gamma-ray Bursts."

Within three hours of the April 23rd burst, Nial Tanvir at the University of Leicester, U.K., and his colleagues reported detection of an infrared source at the Swift position using the United Kingdom Infrared Telescope on Mauna Kea, Hawaii.

At the same time, Fox led an effort to obtain infrared images of the afterglow using the Gemini North Telescope on Mauna Kea. The source appeared in longer-wavelength images but was absent in an image taken at the shortest wavelength of 1 micron. This "drop out" corresponded to a distance of about 13 billion light-years.

An artist's concept of a gamma-ray burst in action. Click on the image for animations. Credit: NASA/Swift/Cruz deWilde.

As Fox spread the word about the record distance, telescopes around the world turned to observe the afterglow before it faded away.

At the Galileo National Telescope on La Palma in the Canary Islands, a team including Guido Chincarini at the University of Milan-Bicocca, Italy, determined that the afterglow's redshift was 8.2. Tanvir's team, gathering nearly simultaneous observations using one of the European Southern Observatory's Very Large Telescopes on Cerro Paranal, Chile, arrived at the same number.

"It's an incredible find," Chincarini says. "What makes it even better is that a telescope named for Galileo made this measurement during the year in which we celebrate the 400th anniversary of Galileo's first astronomical use of the telescope."