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Supernova helps measure the cosmos.

Observations of stellar eruptions billions of light-years from Earth can help determine whether the cosmos will expand forever or eventually collapse. The recent discovery of the most distant supernova explosion known is moving astronomers closer to forecasting the evolution of the cosmos.

Researchers observed the faraway supernova last April with the Isaac Newton telescope in the Canary Islands, Spain. The explosion took place in a galaxy some 5 billion light-years from Earth, meaning that light from the supernova took 5 billion years to reach terrestrial telescopes. The most distant supernova previously detected was located about 4 billion light-years from Earth.

Researchers strongly suspect that the distant supernova belongs to a special class known as 1, triggered when mass is dumped onto a white dwarf star. All 1A supernovas attain the same peak intrinsic brightness - the brightness they would appear to have if an observer were standing right in front of them. Thus, knowing that the luminosity of a star declines in proportion to the square of its distance from Earth, astronomers can use type 1A supernovas as yardsticks to measure several key parameters of the age and expansion of the universe.

One of these numbers is the deceleration parameter, [q.sub.0]. This parameter indicates whether clumps of matter in the universe will continue to move apart fast enough to escape gravity or whether the overall density of the cosmos is so great that it has begun to put the brakes on the expanding universe, dooming the Universe to eventual collapse.

Saul Perimutter of the University of California, Berkeley, and Lawrence Berkeley Laboratory and his colleagues caution that they aren't positive the supernova they observed is a 1A. Moreover, the amount of dust that lies between the supernova and Earth is uncertain, which could confound measurements by making the explosion appear dimmer - and thus more distant- than it really is. But at the moment, their best estimate is that the deceleration parameter seems consistent with a universe poised between permanent expansion and collapse a model popular among theorists.

Perimutter says that his team is searching for other distant, 1A supernovas. In comparing these faraway outbursts with the newly discovered explosion, the team hopes to find a much more definitive value for the deceleration parameter.
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Title Annotation:1A supernova suggests universe is balanced between permanent expansion and collapse
Author:Cowen, Ron
Publication:Science News
Article Type:Brief Article
Date:Jan 23, 1993
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