25 May 1999
Universe 12 Billion Years Old
A team of NASA experts announced recently that the universe might not be as old as was once thought. Their precise measurements of the distance to certain stars suggest the age of the universe is 12 billion years old, considerably younger than was previously held. However, other experts immediately questioned the claim, leaving doubt over one of the basic questions in astronomy.
A team of 27 astronomers led by Wendy Freedman of the Carnegie Institute of Washington, announced completion of an eight-year effort to measure the distance to 800 special stars in order to calculate the speed at which all of the galaxies in the universe are moving apart.
According to Freedman, calculating that separation speed, called the Hubble constant, was a top priority of NASA's space telescope because the result is a critical factor in determining the age of the universe. The Hubble constant was determined to an accuracy of 10 percent and when this value is combined with other measurements it gives an estimated age of the universe of about 12 billion years.
This number may rise slightly, to perhaps, 13.5 billion years if assumptions about the amount of matter in the universe change with further study.
NASA's announcement was quickly denounced by Allan Sandage, a legendary astronomer and head of a Carnegie Observatories team in California that has searched for the Hubble constant since 1968.
"If NASA is giving the impression that the problem is solved, then we would dispute that,"Sandage said. "They have announced a final number and they are not correct."
Astronomers have been searching for the Hubble constant since 1929 when astronomer Edwin Hubble first found that distant galaxies are moving away from the Earth faster than are nearby galaxies.
Astronomers express the Hubble constant by measuring the acceleration rate for every 3.26 million light years in distance.
Calculations using ground telescopes have ranged up to 558, but Freedman said new measurements taken with the space telescope has refined acceleration rate to 70 kilometers per second. This means that a galaxy is moving 160,000 miles per hour faster for every 3.3 light years it is away from the Earth. Freedman said her figure was accurate within 10 percent.
Sandage said NASA's new number is still too high.
"We've said all along that the correct number is about 55," he said. This would give an age of the universe of 14 to 18 billion years, depending on what is assumed about the mass in the universe.
The expanding universe supports the Big Bang theory, the idea that the universe began when all matter was compressed into a single point that then exploded. The theory states that the universe has been expanding ever since.
Recent studies also have shown that the universe probably will expand forever. Some researchers also believe that the expansion is speeding up due to a force that accelerates matter. Existence of this force is still controversial.
Freedman said that the age of the universe would finally be determined when other researchers have more precisely measured the mass and the effect of the mysterious force.
The NASA team reached their Hubble constant number by measuring the distance to a type of star, called a Cepheid, that pulsates at a known rate and strength. By measuring Cepheids in 18 galaxies out to 65 million light years, said Freedman, the team established the rate of expansion.
Sandage said his team measured distances to nine star explosions, called supernovae, and then confirmed these distances with Cepheid measurements. He said this method is more accurate.
Both teams used the Hubble Space Telescope, which can study stellar detail that is unseen by ground telescopes.