Roanoke Times Copyright (c) 1995, Landmark Communications, Inc. DATE: SUNDAY, January 16, 1994 TAG: 9401160049 SECTION: NATIONAL/INTERNATIONAL PAGE: A3 EDITION: STATE SOURCE: Associated Press DATELINE: WASHINGTON LENGTH: Medium
The effect is what would be expected for gamma rays originating from great distances and is consistent with the general theory of relativity, said Jay Norris of the Goddard Space Flight Center in a report prepared for a meeting Saturday of the American Astronomical Society.
The finding also supports the theory that gamma ray bursts occur throughout the cosmos, and not just in the Milky Way as some researchers have suggested.
Norris heads a team at Goddard that analyzed signals from the Compton Gamma Ray Observatory, one of NASA's orbiting astronomy spacecraft. The Compton measures radiation called gamma rays in the short wavelength end of the electromagnetic spectrum.
Gamma-ray bursts are extremely powerful explosions that can be detected only in the gamma-ray portion of the spectrum. The bursts last from a few seconds to a few minutes and during that time their power overwhelms any other source of gamma rays. The sources of the natural gamma ray bursts are not known.
The bursts were first discovered in the 1960s by defense satellites. It was first believed that they originated only from the Milky Way Galaxy because they were so powerful.
But NASA's Compton Observatory has shown that the signals come from all directions and from every part of the universe.
Norris' study shows they also come from extremely far away.
The gamma rays analyzed by Norris and his team show a distinct difference in the duration of the signal pattern between bright gamma ray bursts and dim gamma ray bursts. If the signals came from the same distance and varied only by intensity, the pattern would be the same.
Norris said the signals also were stretched out. This means the distance between electromagnetic wave peaks is slightly elongated, a change called red-shifting. He said this time dilation effect is caused by signals traveling great distances across a universe that may be expanding.
"Our results should not be taken as proof that the time-dilation is a result of cosmological expansion of the universe - just that a difference in durations of bright and dim bursts does exist and must now be accounted for by any theory," Norris said in a statement.
Bohdan Paczynski of Princeton University, who had predicted such an effect on gamma ray bursts, said the finding is "one of the most spectacular astrophysical discoveries of the decade."
Virginia Trimble of the University of California, Irvine, said astronomers have been searching for markers caused by the immensity of the universe, the so-called "cosmological effects."
"If the gamma bursts have indeed revealed such cosmological effects, then this is perhaps even more important as an astrophysical `first' than as a contribution to our understanding of the bursters themselves," she said in a statement released through NASA.
by CNB