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SWIFT Captures an Expolding Star at the Edge of the Visible Universe

11/24/2005 08:11AM

SWIFT Captures an Expolding Star at the Edge of the Visible Universe
Scientists using the NASA Swift space-based observatory and several ground-based telescopes have detected the most distant explosion yet, a gamma-ray burst from the edge of the visible Universe.

This powerful burst, marking the death of a massive star and the birth of a black hole, comes from an era soon after stars and galaxies first formed, about 500 million to 1 billion years after the Big Bang. The science team cannot yet determine the nature of the exploded star -- a detailed analysis is forthcoming.

This is uncharted territory, said Dr Daniel Reichart of the University of North Carolina (UNC) at Chapel Hill, who spearheaded the distance measurement. This burst smashes the old distance record by 500 million light years. We are finally starting to see the remnants of some of the oldest objects in the Universe.

Professor Keith Mason, UK lead scientist on the Ultra Violet/Optical Telescope on Swift and Chief Executive of the Particle Physics and Astronomy Research Council said, "This is an amazing result that will enable us to find out more about stars from near the beginning of time. Swift is operating brilliantly -- first detecting the gamma rays bursts and then alerting telescopes across the world to enable follow up observations -- a truly international mission combining space and ground based astronomy."

Only one quasar has been discovered at a greater distance. Yet whereas quasars are supermassive black holes containing the mass of billions of stars, this burst comes from a single star. Scientists say that it is in fact puzzling how a single star could generate so much energy as to be seen across the entire Universe. This early star is perhaps physically different from the kinds of stars that exist today.

Scientists measure cosmic distances via redshift, the extent to which light is shifted towards the red (lower energy) part of the electromagnetic spectrum during its long journey across the Universe. The greater the distance the higher the redshift.

This burst, named GRB 050904, had a redshift of 6.29, which translates to a distance of about 13 billion light years from Earth (the Universe is thought to be 13.7 billion years old). The previous most distant gamma-ray burst had a redshift of 4.5. The most distance quasar known is at redshift 6.4. GRB 050904 was also very long, lasting over 200 seconds. Most bursts last only about 10 seconds.

Swift detected the burst and relayed its coordinates to scientists around the world within minutes. Reichart's team at UNC discovered the afterglow with the Southern Observatory for Astrophysical Research (SOAR) telescope atop Cerro Tololo, Chile. Over the next several nights, the UNC team used SOAR and the Gemini South telescope, on Cerro Pachon, to calculate a redshift of 6 via a light filtering technique.

Dr Nial Tanvir from the University of Hertfordshire, observed the afterglow of the burst on the United Kingdom Infrared Telescope and Gemini South comments "How a single star could generate so much energy as to be seen across the whole of the Universe remains an unanswered question. The fact that we can see it now may provide us with a new tool to help understand those very early times."

Gemini South Associate Director, Phil Puxley, comments on the key observations at Gemini South, "Timing is everything when it comes to making an observation like this - this is short-order astronomy! Getting good data is always rewarding but when we can catch something as fleeting as a Gamma-Ray Burst the thrill of the chase is added to the mix."

Building upon these measurements, a team led by Nobuyuki Kawai of the Tokyo Institute of Technology used the Subaru Observatory on Mauna Kea, Hawaii, to confirm the distance and fine-tune the redshift measurement to 6.29 via spectroscopy.

A team of Italian astronomers, using one of four 8.2 metre telescopes that comprise the European Southern Observatorys Very Large Telescope (VLT) observed the object in the near-infrared and in the visible. By comparing the brightness of the source in the various bands, the astronomers could deduce its redshift and, hence, its distance. The value they derived was confirmed by the spectroscopic observations made by the team using the Subaru telescope.

SWIFT is a unique space-based observatory developed by an international team from the United States, the United Kingdom, and Italy, with additional scientific involvement by France, Japan, Germany, Denmark, Spain, and South Africa. It is the first multi-wavelength observatory dedicated to the study of gamma-ray burst science.
"We designed Swift to look for faint bursts coming from the edge of the Universe," said Dr Neil Gehrels of NASA, Swift Principal Investigator. "Now we've got one and it's fascinating. For the first time we can learn about individual stars from near the beginning of time. There are sure to be many more out there."

The detection of GRB 050904 confirms that massive stars mingled with the oldest quasars and that even more distant star explosions, perhaps from the first stars, can be studied through a combination of Swift and the network of world-class telescopes.