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17 April 2014 12:48 pm ,
Vol. 344 ,
Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Gamma Ray Needles May Pierce Space
12 September 2003 (All day)
Gamma ray bursts (GRBs) and other cosmic explosions called x-ray flashes are the same phenomenon in different guises. That's the prediction of a disputed new model in which GRBs--the most powerful explosions in the universe--aim their energy like a rifle shot, whereas x-ray flashes emit broader fans of energy. If true, up to 100,000 GRBs could blow up in the universe for each one that astronomers see.
Satellites spot GRBs as flares of the most energetic radiation known. Astronomers reached a consensus about their origins earlier this year by finding the signature of an exploded star--a supernova--at the site of a nearby GRB (ScienceNOW, 14 April). Theorists now concur that massive stars must spew fantastic jets of energy into space when their cores collapse into black holes, but they disagree about what those jets look like. Clues lie in comparing GRBs to their seemingly less-energetic cousins, x-ray-rich GRBs and x-ray flashes, whose sources are more mysterious.
New research suggests all three types arise from supernovas that focus their fury in jets with drastically different shapes. Astrophysicist Donald Lamb of the University of Chicago and colleagues examined the energies of GRBs and their x-ray kin recorded by the High-Energy Transient Explorer-2 (HETE-2) satellite and earlier orbiters. The team saw a tight correlation between the total energy observed for each blast and the peak wavelength of the measured radiation. The bursts that appeared to be the most powerful churned out most of their energy in intense, short-wavelength gamma rays, while the weakest ones had peak energies at longer wavelength x-rays.
This striking pattern implies that the three types of explosions all have the same overall energy. If that's the case, says Lamb, an x-ray flash must spew radiation in nearly all directions, dimming its impact for a distant observer. However, a GRB would channel its outburst into a needlelike cone perhaps 1 angular degree wide, which we see as a far brighter flare. "Their jets are so tiny that we only see them if we are in the boresight," says Lamb, noting that we would detect just one of every 10,000 or 100,000 such blasts. Lamb spoke on 11 September at the GRB 2003 Symposium in Santa Fe, New Mexico.
His scenario earned a mixed reception. Astronomer Dale Frail of the National Radio Astronomy Observatory in Socorro, New Mexico, says the unified model "is so simple and elegant, you want it to be true." But astrophysicist Shrinivas Kulkarni of the California Institute of Technology in Pasadena objects to the "incredibly tiny" 1-degree beams. Rather, his group's research points to a range of gamma ray and x-ray energies emerging together in wider cones.