Spiral galaxy NGC 4603 is the most distant galaxy in which a special class of pulsating stars have been found. (Reuters)

By Kathy Sawyer
Washington Post Staff Writer
Wednesday, May 26, 1999; Page A1

Astronomers announced yesterday they have taken a giant step toward solving a major question about the universe, determining with unprecedented accuracy the rate at which cosmic objects are flying apart – a number that is key to understanding the age, size and fate of all creation.

The result, reached by the Hubble Space Telescope Key Project Team, dates the birth of the universe in a "big bang" explosion at between 12 billion and 13.5 billion years ago, or much more recent than once thought. Independent scientists said the finding also fits with growing evidence that the expansion of the universe is accelerating and is likely to continue virtually to infinity rather than collapsing back on itself in a gravitational "big crunch."

For most of this century, astronomers have tried to take the measure of the hurtling universe in this way, but it was too vast for the instruments and techniques that existed as recently as the 1980s. The quest for this number, a fundamental of nature, was a driving force behind the construction of the $2.2 billion Hubble Space Telescope.

"After all these years, we are finally entering an era of precision cosmology," said Wendy Freedman, of the Observatories of the Carnegie Institution of Washington, a leader of the large international research team. "Now we can more reliably address the broader picture of the universe's origin, evolution and destiny."

While a long-running and sometimes heated feud over the age of the universe is sure to continue, scientists said, the findings narrow the range of the disagreement for the first time to the mere normal "rough and tumble" of scientific debate.

The Hubble team spent eight years and accumulated some 400 hours of observations with the orbiting telescope, which views the cosmos in fine detail above the distortions of the Earth's atmosphere. They took meticulous measurements of 800 special "cosmic yardstick" stars, known as Cepheids, in a sampling of 18 galaxies ranging over a swath 150 million light-years across. They then combined their Cepheid technique with four different methods to gauge distances farther and farther out into space.

All four methods yielded the same number, said team co-leader Jeremy Mould, of the Australian National University. Galaxies are rushing away from each other at a rate that increases by "70 kilometers (44 miles) per second per megaparsec," with an uncertainty of 10 percent. (A megaparsec is 3.26 million light-years, and each light-year – the distance light travels in one year – is 5.9 trillion miles.)

Translated, this means that a given galaxy appears to be moving 160,000 miles per hour faster for every 3.3 million light-years it travels away from Earth.

"This has been a marathon," Mould said. Today, "we feel we've cut the tape."

The Hubble team's number still differs from that of a rival "older universe" camp, led by scientist Allan R. Sandage, a colleague of Freedman's at the Carnegie Observatories offices in Pasadena, Calif. Sandage disputes the new findings. Having worked on the problem for a quarter of a century and produced numerous papers of his own, Sandage, who also uses the Hubble telescope but not the same technical approach, said recently that his numbers call for a cosmic age closer to 14.5 billion or 15 billion years – or even older, depending on what other assumptions are made about the universe.

Scientists "used to disagree by a factor of two," said Robert Kirshner, of Harvard University, who is not on either the Freedman or Sandage teams. That was a huge gap, like "arguing about having one foot or two," he said. But now the range of difference has been narrowed to a mere 10 percent, which is more "like a difference of one toe. This is good to plus or minus one piggy."

Kirshner said his own work with a different type of yardstick – brilliant but rapidly fading exploding stars – had produced a number (64 km or 40 miles per second, etc.) comfortably in the middle between those of Freedman and Sandage.

Other research teams, including those who published findings in the May 29 issue of the journal Science, differ slightly from the Hubble team but are in the same general range.

This "convergence" of data also accommodates the oldest stars in the universe, scientists said. Earlier estimates had created some turmoil by seeming to show that the universe might be younger than its own oldest inhabitants. "It feels great to reach this point," Freedman said. Managing the project with so many astronomers has been somewhat "like herding cats."

Theorist Michael Turner of the University of Chicago, who is not on either team, praised the Freedman group for its meticulous attention to determining the degree of uncertainty in its Hubble constant finding – something he said previous researchers had not always done despite its importance. "It's thankless work, it takes an extra year and no papers come out" for publication.

Measuring the Hubble constant to this degree of accuracy is a "major milestone," Turner said.

Like projectionists rewinding a movie, the researchers use the Hubble constant – the expansion rate – to determine the proper "rewind" speed of the big bang explosion from which all of time and space are believed to have sprung.

Both the number and the telescope are named after the same American astronomer, Edwin Hubble, who in 1929 provided the first observational evidence for a monumental new idea: that the universe was not peaceful and unchanging, but was evolving. He proposed that galaxies were rushing away from each other and that the farther apart they were, the faster they were separating. Ever since then, a long line of distinguished scientists has struggled with a pageant of wildly varying numbers for that outrushing.

As recently as the 1980s, "astronomers could not decide if the universe was 10 billion or 20 billion years old," said Freedman.

The quest for the magic number drove the design of the Hubble telescope, for example setting the minimum diameter of its primary mirror, said NASA chief scientist Edward J. Weiler. The telescope was "sold" to Congress in part based on that capability. Yesterday's presentation at NASA headquarters marked the culmination of some two decades of planning and painstaking research, he added, and is largely the story of "27 astronomers in search of that number."

Freedman and others noted that nailing down the age of the universe even more precisely depends on other factors and interpretations, such as the density of matter (and therefore the gravitational power attracting objects toward each other) in the universe, which is still uncertain; and whether there is, as some evidence suggests, an exotic energy in the "vacuum" of space that is working against gravity to repel objects apart. This issue remains controversial.