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			What do gamma-rays show us? Beck Bray & Patrick Meyer 01.27.01 If you could see gamma-rays, the night sky would look strange and unfamiliar. The familiar sights of constantly shining stars and galaxies would be replaced by something ever-changing. Your gamma-ray vision would peer into the hearts of solar flares, supernovae, neutron stars, black holes, and active galaxies. Gamma-ray astronomy presents unique opportunities to explore these exotic objects. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments which are not possible in earth-bound laboratories. Perhaps the most spectacular discovery in gamma-ray astronomy came in the late 1960s and early 1970s from a constellation of defense satellites which were put into orbit for a completely different reason. Detectors on board the Vela satellite series, designed to detect flashes of gamma-rays from nuclear bomb blasts, began to record bursts of gamma-rays -- not from the vicinity of the Earth, but from deep space! Today, these gamma-ray bursts, which happen at least once a day, are seen to last for fractions of a second to minutes, popping off like cosmic flashbulbs from unexpected directions, flickering, and then fading after briefly dominating the gamma-ray sky. Gamma-ray bursts can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! So far, it appears that all of the bursts we have observed have come from outside the Milky Way Galaxy. Scientists believe that a gamma-ray burst will occur once every few million years here in the Milky Way, and in fact may occur once every several hundred million years within a few thousand light-years of Earth. Studied for over 25 years now with instruments on board a variety of satellites and space probes, including Soviet Venera spacecraft and the Pioneer Venus Orbiter, the sources of these enigmatic high-energy flashes remain a mystery. There are several theories currently discussed as possible causes of gamma-ray bursts. One explanation proposes that they are the result of colliding neutron stars. A second theory proposes that gamma-ray bursts are the result of a merging between a neutron star and a black hole or between two black holes. A new theory that is attracting considerable attention states that gamma-ray bursts occur as the result of material shooting towards Earth at almost the speed of light as the result of a hypernova. A hypernova explosion can occur when the largest of the supermassive stars come to the end of their lives and collapse to form black holes. Hypernova explosions can be at least 100 times more powerful than supernova explosions. By solving the mystery of gamma-ray bursts, scientists hope to gain further knowledge of the origins of the Universe, the rate at which the Universe is expanding, and the size of the Universe.


			Š2001 NASAkids.com , Science@NASA Beck Bray & Patrick Meyer