Universe Will Expand Forever, Astronomers Say
(From the March/April 1998 issue of StarDate magazine)
Our universe will expand forever, according to several groups of astronomers who have studied exploding stars, giant galaxies, and the structure of the early universe.
Most astronomers agree that the universe was born in the Big Bang, and that it continues to expand as a result of the initial "kick" from the Big Bang. But there is disagreement over the fate of the universe. If the universe contains enough matter, gravity will halt the expansion and bring the universe crashing in on itself in a "Big Crunch" -- the reverse of the Big Bang. But if there is insufficient matter, the universe will continue to expand forever.
Ruth Daly and Eric Guerra of Princeton University studied the geometry of the universe by measuring the sizes and distances to 14 galaxies that produce large amounts of radio energy. From these observations, "we can state with 95 percent confidence that the universe will continue to expand forever," said Daly. It will expand at a faster and faster rate as time goes by, she added.
Another Princeton team, headed by Neta Bahcall, found that the universe contains only about 20 percent of the mass needed to stop its expansion.
Bahcall's team counted the number of large galaxy clusters seen at different distances, which means at different times in the history of the universe. They found that many large clusters existed in the very early universe, which means the universe is "lightweight."
Several other teams are trying to measure the size, age, and expansion rate of the universe by studying a particular variety of supernova -- a star that blows itself to bits, briefly outshining an entire galaxy of billions of normal stars. Such stars are so bright that they are visible across million or billions of light-years.
Three groups of astronomers reported that their observations of these stars indicate the universe is about 12 billion to 15 billion years old.
Recent Hubble Space Telescope studies of other types of distant stars had indicated that the universe is much younger -- younger than many of its stars, in fact. But the supernova studies (some of which also use HST observations) contradict that idea.
However, additional observations of the other class of stars continue to show a younger age, according to members of the research team. Many more observations will be needed to settle the debate over the age of the universe. -- — Damond Benningfield
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