News Release

Most distant explosion in universe to date has been detected;
UNC research team led distance measurement with SOAR

CHAPEL HILL -- A University of North Carolina at Chapel Hill research team measured the distance of an explosion scientists recently determined to be the farthest ever detected: a gamma-ray burst from the edge of the visible universe.

Scientists using the NASA Swift satellite and several ground-based telescopes detected this powerful burst – likely marking the death of a massive star as it collapsed into a black hole – on Sept. 4.

Just three hours after the discovery, a network of observers led by Dr. Daniel Reichart, assistant professor of physics and astronomy within UNC’s College of Arts and Sciences, used the OSIRIS infrared instrument on the Southern Observatory for Astrophysical Research (SOAR) telescope to detect the afterglow of the gamma-ray burst.

UNC undergraduate Josh Haislip was the first to analyze the SOAR data. Haislip, a junior from Williamston, will be first author on the pending research publication. Other UNC students who played key supporting roles are graduate student Melissa Nysewander, and seniors Chelsea MacLeod of Hillsborough and Justin Kirschbrown of Charlotte.

The SOAR telescope is situated on Cerro Pachon, Chile, at an altitude of 8,775 feet above sea level, at the western edge of the Chilean Andes’ jagged peaks. The telescope is a public-private partnership among UNC, the U.S. National Optical Astronomy Observatory (NOAO), the Ministry of Science of Brazil and Michigan State University.

The newly detected powerful burst 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 Reichart. "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."

Indeed, only one quasar has been discovered at a greater distance. Whereas quasars are supermassive black holes containing the mass of billions of stars, this newly discovered burst comes from a single star.

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

Named GRB 050904, the newly discovered object has 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. GRB 050904 also was very long in duration, lasting more than 200 seconds; most bursts last only about 10 seconds.

Scientists on four continents using a multitude of telescopes tracked the burst and its afterglow for days as the burst gradually faded, a true worldwide effort. The discovery is being heralded as a major breakthrough in the study of the early universe. Few quasars are seen at exceedingly far distances, or the earliest epoch of star and galaxy formation, despite exhaustive searches.

Yet gamma-ray bursts might be plentiful, said Dr. Donald Lamb, professor of astronomy and astrophysics at the University of Chicago, who with Reichart had predicted the detection of very distant gamma-ray bursts.

"This is what we’ve been hoping and waiting for," Lamb said. He added that he anticipates the discovery of scores, if not hundreds, of very distant gamma-ray bursts in the coming years.

These bursts would provide information about where and when the earliest stars formed and what chemical elements they produce when they explode. Traveling across the entire universe, the light from the bursts would also contain information about all the material it passed through on its long journey toward Earth.

Swift detected GRB 050904 and relayed its coordinates to scientists worldwide in about 20 seconds. Gamma-ray bursts disappear quickly, which is why Swift was designed to autonomously detect and locate bursts and notify the science community via e-mail, Web sites and even cell phone.

"We designed Swift to look for faint bursts coming from the edge of the universe," said Dr. Neil Gehrels of NASA Goddard Space Flight Center in Greenbelt, Md. Gehrels is the 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 surely many more out there."

Reichart’s team at UNC was one of the first groups to respond to the alert. The team discovered the afterglow with SOAR. Over the next several nights, the team used SOAR and the Gemini South telescope, also on Cerro Pachon, to calculate a redshift of greater than 6 via a light filtering technique.

"The earliest stars exploded eons ago; we know very little about them," said UNC’s Haislip. "One of the best ways we can study them is by watching for their explosions. Swift can pinpoint the location of the explosions, and telescopes such as SOAR can study the composition of the debris to understand where and when these stars formed and what they were made of."

The observations of SOAR were made by Eduardo Cypriano and Elysandra Figueredo of Brazil, working from the telescope’s remote observing room about a two-hour drive away in La Serena, Chile. They were connected by videoconference to the SOAR telescope operators on Cerro Pachon and to the UNC team.

Reichart directs a new array of six small automated telescopes at nearby Cerro Tololo Inter-American Observatory, called the Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT). He searched for the afterglow with PROMPT, which didn’t find it – providing evidence that this was a very distant burst redshifted to an infrared energy below PROMPT’s range in visible light.

"This is when we got really excited, because this is exactly the sort of signature that you are hoping for if you are looking for very distant objects," Reichart said.

UNC received two National Science Foundation grants totaling $912,000 to build PROMPT, which was designed specifically to study gamma-ray bursts. Research collaborators are Appalachian State University, Elon University, Fayetteville State University, Guilford Technical Community College, N.C. Agricultural and Technical State University, UNC-Asheville, UNC-Charlotte, UNC-Greensboro, UNC-Pembroke and Western Carolina University, as well as Hampden-Sydney College in Virginia. 

PROMPT and SOAR have both been in operation since 2004.

"SOAR is a new telescope that is still in the advanced commissioning phase," Reichart said. "The instrument that we used, OSIRIS, was just put on the telescope and made available for science observations a few days before this event. In fact, I had asked Josh [Haislip, a UNC undergraduate] to do some extra research on the instrument to be prepared just in case, since my more senior students were away at a gamma-ray burst workshop! He and the other students on the team did an excellent job and are now well-prepared to work on future bursts with SOAR and PROMPT."

- 30 -

Related links:
SOAR dedication: http://www.unc.edu/news/archives/apr04/soarmain041604.html
PROMPT: http://www.unc.edu/news/archives/aug04/prompt080504.html
Bio and photo of Reichart: https://s4.its.unc.edu/UNCExperts/uncexperts/getperson?ID=RWVCFDDWF
SOAR telescope information: http://www.soartelescope.org
SOAR image: http://www.noao.edu/image_gallery/html/im0858.html

Note: Contact Reichart at reichart@physics.unc.edu. Animation and still graphics related to this discovery are scheduled to be posted at the following NASA Web site: http://www.nasa.gov/vision/universe/starsgalaxies/2005_distant_grb.html

NASA contact: Dolores Beasley, (202) 358-1753 or dbeasley@nasa.gov
UNC News Services contact: Deb Saine, (919) 962-8415 or deborah_saine@unc.edu
UNC College of Arts and Sciences contact: Dee Reid, (919) 843-6339 or deereid@unc.edu