Originally created 09/23/99

Universe may be younger than thought



The celestial yardstick most commonly used for measuring the universe may have to be recalibrated.

That's the upshot of an analysis by a team of astronomers, who worked with new, more precise measurements of the distance to a far-off galaxy.

If their analysis is correct, the universe may be expanding faster and could be somewhat younger than currently thought, the researchers reported in Thursday's issue of the journal Nature.

Ever since Edwin Hubble discovered the universe was expanding in 1929, astronomers have sought to determine the rate of that expansion, called the Hubble constant, and whether the universe will continue expanding or eventually collapse in on itself. Over the past five years, astronomers have come up increasingly more accurate measurements, and some believe their estimates are within 10 percent of the actual rate.

To reach these estimates, astronomers measure and compare distances to certain flickering stars called Cepheid variables. Astronomers use the brightness of Cepheids observed in far-off galaxies and compare them with Cepheids in a galaxy known as the Large Magellanic Cloud.

For example, if a Cepheid variable in a galaxy of unknown distance is one fourth as bright as a Cepheid in the LMC, that galaxy is twice as far away as the LMC. The drop in brightness is always the inverse of the square of the distance -- a Cepheid in a galaxy three times as far away will be one ninth as bright.

The problem, however, has been determining the distance to the LMC, which has been measured only to within 10 percent accuracy.

NASA researcher Eyal Maoz and his colleagues tried to get around the problem by using new, more precise measurements to another galaxy altogether, known as NGC4258. These measurements are believed to be accurate to within 4 percent.

These new findings indicate "something is probably wrong with the Cepheid calibration," said Maoz, who is at NASA's Ames Research Center at Moffett Field, Calif. "If it is correct, it has significant implications for our understanding of the universe."

If Cepheid distances are revised according to his findings, the rate at which the universe expands would increase 12 percent, plus or minus 9 percentage points. The age of the universe, meanwhile, would decrease by the same amount from the current estimate of 12 billion to 13 billion years.

"It will take some time for the community to digest this, but it's definitely shakng the boat right now," Maoz said.

"Galaxy NGC4258 may turn out to be a better yardstick," Princeton University astronomer Bohdan Paczynski wrote in an accompanying commentary. But he said that because of other recently discovered errors in celestial observations, the mistakes may cancel themselves out and the Hubble constant may not need to be revised after all.

Michael Turner, chairman of astrophysics at the University of Chicago, said the significance of Maoz's work is unclear because of the large margin of error in the findings.

"The correction could be 12 percent plus or minus 9 percent," Turner said. "That means it could be almost zero as likely as it could be 20 percent."