A mystery as old as universe is solved -- maybe

May 26, 1999
by Paul Hoversten

Scientists using the Hubble Space Telescope announced Tuesday that they had at last determined an age for the universe: 12 billion to 13.5 billion years. Like many scientific pronouncements, the findings were immediately disputed.

Breakthrough: Stars of galaxy NGC 4603 gave clues

The reason for the intense interest in the subject is that an accurate measurement would allow astronomers to accurately develop a broader picture of the universe's beginning, evolution and end.

Scientists have theorized that the universe will expand indefinitely. It will appear more and more sparse as galaxies move farther from one another, but there is no danger of it collapsing back on itself, they say.

"We've now measured the expansion rate to within 10% accuracy, which was our objective," says Hubble team leader Wendy Freedman of the Observatories of the Carnegie Institution in Washington. "We've been able to break an impasse."

Not to the satisfaction of Allen Sandage, head of a Carnegie Observatories team in Pasadena, Calif. His team has been researching the matter since 1968, and he says his calculations point to between 14 billion and 18 billion years.

"If NASA is giving the impression that the problem is solved, then we would dispute that," Sandage says.

Freedman's team spent eight years using Hubble to look at 18 galaxies as far as 65 million light-years from Earth. In those galaxies, the scientists found 800 Cepheid variable stars, rare pulsating stars used to measure vast distances.

	What is the Hubble Constant? Who was Edwin Hubble? What is a light-year? What did Hubble telescope scientists use to calibrate their measurements? Try It! A light-year is the distance light travels in a vacuum for one year. Determine the number of miles in one light-year, and write down the numbers as figures. The Hubble Constant -- which indicates the rate at which the universe is expanding -- is now estimated to be about 44 miles per second per megaparsec of distance. A megaparsec is 3.26 million light-years. Determine the number of miles in 3.26 million light-years, then write down the numbers as figures. What does this new information about the universe tell us about our neighboring galaxies and the longevity of matter?

The team, made up of 27 astronomers from 13 different U.S. and international institutions, used those stars to calibrate different methods to come up with an age of 12 billion to 13.5 billion years.

"This is the most important discovery in physical science ever, that we live in an expanding universe," says Robert Kirshner, an astronomer at Harvard University.

Whereas scientists used to disagree about the universe's age by a factor of two, Freedman's team has cut the error margin to just 10%.

Until the launch of Hubble in 1990, astronomers could not decide whether the universe was 10 billion or 20 billion years old. Freedman's team was able to calculate not only the age of the universe but also its expansion rate: A galaxy appears to be moving 160,000 mph faster for every 3.3 million light-years it is from Earth. A light-year is the distance light travels in a year, about 6 trillion miles.

The findings complete what astronomers consider the prime task for the Hubble.

"Out of 20 scientific problems we posed for the Hubble telescope, this was No. 1," says Ed Weiler, NASA's space science chief. "This is Hubble's greatest contribution to the field of astronomy."