UNIVERSITY PARK – Tantalizing insights into the nature of the most distant object ever observed in the universe have been achieved by an international research team whose leaders include Derek Fox, assistant professor of astronomy and astrophysics at Penn State. The team used the National Science Foundation’s Very Large Array (VLA) radio telescope to observe the distant object — a gigantic stellar explosion known as a gamma ray burst (GRB). A scientific report of the team’s findings has been submitted to Astrophysical Journal Letters.
The explosion was first detected on April 23, 2009, by a team of astronomers using NASA’s Swift satellite, whose leaders included David Burrows, senior scientist and professor of astronomy and astrophysics at Penn State. Scientists soon realized that the explosion was more than 13 billion light-years from Earth and that it marks an event that occurred 630 million years after the Big Bang, when the universe was only four percent of its current age of 13.7 billion years. “This object began life as a massive star that lived fast and died young, going out with a stupendous bang. If not for that ‘bang’ — the gamma ray burst — we would still not know that these stars existed so early in the universe,” Burrows said.
Astronomers used telescopes from around the world to study the blast, dubbed GRB 090423. “It is important to study these kinds of explosions with many kinds of telescopes,” Fox said. Images are on the Web. The VLA first looked for the object the day after the discovery, detected the first radio waves from the blast a week later, then recorded changes in the object until it faded from view more than two months later.
“This explosion provides an unprecedented look at an era when the universe was very young and also was undergoing drastic changes,” said
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 those early generations of stars.
“Our research team combined the data from the VLA with that from X-ray and infrared telescopes, allowing us to piece together some of the physical conditions of the blast,” Fox said. “The result is a unique look into the very early universe that we couldn’t have gotten any other way.” The scientists concluded that the explosion was more energetic than most GRBs, was a nearly-spherical blast, and that it expanded into a tenuous and relatively uniform gaseous medium surrounding the star.
Astronomers suspect that the earliest stars in the universe were very different from those that formed later — brighter, hotter and more massive. They hope to find evidence for these giants by observing objects as distant as GRB 090423 or more distant.
“The best way to distinguish these distant, early-generation stars is by studying their explosive deaths, as supernovae or Gamma Ray Bursts,” said Poonam Chandra, of the Royal Military College of Canada, and leader of the research team. 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. 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,” Frail said. Both ALMA and the EVLA are scheduled for completion in 2012.
Chandra, Frail and Fox worked with Shrinivas Kulkarni of Caltech, Edo Berger of Harvard University, S. Bradley Cenko of the University of California at Berkeley, Douglas C.-J. Bock of the Combined Array for Research in Millimeter-wave Astronomy in California, and Fiona Harrison and Mansi Kasliwal of Caltech.
Penn State researchers on the team that discovered the record-breaking GRB 090423 and measured its distance (results will be published in the Oct. 29 issue of the journal Nature) include Burrows; Jamie Kennea, XRT instrument scientist; Fox; and Nino Cucchiara, graduate student.
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities Inc. Swift is a NASA satellite, built in collaboration with with partners at Penn State, in Italy and in the United Kingdom, whose science and flight operations are controlled by Penn State from the Mission Operations Center in State College, Pa.
