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NASA ANNOUNCES DETECTION OF MOST DISTANT EXPLOSION

Media teleconference time: 2 p.m. EDT

Date: Monday, September 12, 2005

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Dolores Beasley at (202) 358-1753 or Erica Hupp at (202) 358-1237

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Password For Both - SWIFT



Most Distant Explosion Detected, Smashes Previous Record

Scientists detected the burst using NASA's Swift satellite. Several ground-based telescopes, including the international Southern Observatory for Astrophysical Research (SOAR) in Chile, measured the astounding distance as the embers faded.

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Shows the counting rate in the gamma-ray instrument on Swift for two gamma-ray bursts. The top panel is for the high redshift burst observed on September 4, 2005 (GRB 050904). The bottom panel shows a typical burst for comparison; it is the one Swift detected on March 26, 2005 (GRB 050326). GRB 050904 is fainter and much longer than typical.Image credit: Dr. Neil GehrelsNearly 13 billion years ago, an early massive star explodes. The light from the explosion, called a gamma-ray burst, traverses the Universe. On September 4, 2005, the NASA Swift satellite detects the burst and notifies scientists of its location. Scientists using the Southern Observatory for Astrophysical Research (SOAR) telescope atop Cerro Pachon, Chile, discover the burst afterglow and, with the help of other telescopes and science teams, nail down the distance. At redshift 6.29, the burst is by far the most distant known.Credit: Trent Schindler/NSFStars shine by burning hydrogen. The process is called nuclear fusion. Hydrogen burning produces helium "ash." As the star runs out of hydrogen (and nears the end of its life), it begins burning helium. The ashes of helium burning, such as carbon and oxygen, also get burned. The end result of this fusion is iron. Iron cannot be used for nuclear fuel. Without fuel, the star no longer has the energy to support its weight. The core collapses. If the star is massive enough, the core will collapse into a black hole. The black hole quickly forms jets; and shock waves reverberating through the star ultimately blow apart the outer shells. Gamma-ray bursts are the beacons of star death and black hole birth.Nicolle Rager Fuller/NSFDiscovery image (left panel) of the afterglow of GRB 050904 taken with the 4.1m Southern Observatory for Astrophysical Research (SOAR) telescope at infrared wavelengths. The afterglow can be seen fading away on subsequent nights (right panels, also from SOAR).Dr. Daniel ReichartNon-detection of the afterglow by one of the six 0.41m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) at visible wavelengths helped the University of North Carolina team determine the extreme distance of this event.Dr. Daniel ReichartDiscovery of the first very high redshift GRB opens the door to their use as unique and powerful probes of the early universe. The slide places GRBs in cosmological context and highlights what very high redshift GRBs can tell us about the early universe.At recombination, which occurs at redshift z = 1100, the universe becomes transparent. The cosmic background radiation originates at this redshift. Shortly afterward, the temperature of the cosmic background radiation falls below 3000 K and the universe enters the ``dark ages,'' during which there is no visible light in the universe. ``First light,'' which cosmologists think occurs about z = 20, corresponds to the moment when the first stars form. Ultraviolet radiation from these first stars and from the stars that are born later is thought to re-ionize the universe. Afterward, the universe is transparent in the ultraviolet. GRBs are due to the collapse of massive stars, and are therefore expected to occur out to redshifts of about z = 20 (unlike QSOs or bright galaxies). Both GRBs and their afterglows are very bright, and are therefore easily observed out to z = 20 (unlike QSOs or galaxies).As the light from each GRB afterglow travels to us, it passes through intergalactic gas and galaxies at lower redshifts. These leave their "fingerprints" on the light, telling astronomers about the history of the universe in a way that is analogous to the way that ice cores drilled deep into the Greenland ice cap tell us about the climatic history of the Earth. In particular, very high redshift GRBs are:o markers of the moment of "first light," o tracers of the star-formation history of the universe,o tracers of the elemental abundance history of the universe, and o tracers of the reionization history of the universe.Thus GRBs hold enormous promise as unique and powerful probes of the early universe.Dr. Don Lamb and Dr. Daniel ReichartThe most distant explosion ever detected occurred deep deep deep in the constellation Pisces. The explosion -- a gamma-ray burst, likely from a very early star explosion -- occurred nearly 13 billion years ago, when the Universe was about 6% its current age. The light passed by the Earth on September 4, 2005. A brilliant flash of gamma rays, detected by NASA's Swift satellite, lasted for about 200 seconds. An afterglow in infrared light detected by ground-based telescopes lingered for several days and allowed scientists to measure the distance to the burst.