Universe Far Younger Than Believed, Two Studies Find : Astronomy: Results show cosmos is newer than oldest stars--creating a 'very profound' paradox for scientists.

TIMES SCIENCE WRITER

The universe is a far younger and smaller place than anyone suspected, two independent teams of distinguished astronomers announced Wednesday. In fact, the universe may be only about half as old as the oldest stars and galaxies it contains.

That fundamental paradox--sure to keep philosophers, theologians and astronomers awake at night--is one byproduct of the newest and most accurate estimates of the size and age of the universe.

Taken together, the new findings promise to startle the astronomical world by challenging some long-held assumptions about the properties of the universe, which encompasses all known matter and space, since it evolved from a primeval fireball.

"It gives cosmologists and astronomers the marching orders to go and explain the discrepancy between the oldest stars and the age of the universe," said Stephen Maran, a senior astronomer at NASA's Goddard Space Center and a spokesman for the American Astronomical Society. "There is something very profound going on."

In an often frustrating effort to solve one of nature's most fundamental puzzles, scientists have argued for decades over the age of the cosmos and how fast space itself has expanded since creation.

Astronomers believe the key to any scientific answer is Hubble's constant, which is a measure of the ratio of velocity to distance for remote, receding galaxies. Scientists have been constantly refining their calculation of the constant, based on data gleaned from increasingly precise astronomical observations. The right answer holds the key to whether the universe may one day reach the end of its outward rush, reverse, and slowly collapse in on itself in what some astronomers like to call the Big Crunch.

By radically different routes, the two international teams have arrived at what several experts say are surprisingly similar and unsettling answers.

One group, led by Indiana University astronomer Michael J. Pierce, developed a better yardstick for gauging the size, and hence the age, of the expanding universe by calculating with unprecedented precision the distance to the Virgo Cluster, 50 million light-years away.

Their calculations led them to believe the universe could be as little as 7 billion years old, compared to previous estimates of as much as 20 billion.

The other researchers, led by Harvard University astronomer Robert Kirshner, used five exploding supernovas as surveyor's marks to calculate the cosmic distance scale. That group found the universe to be between 9 billion and 14 billion years old, but still much younger than previously believed.

The Indiana study appears in today's issue of Nature and the Harvard research is published in the current issue of the Astrophysical Journal.

Although the studies disagree in their age estimates, several experts said, they both determined very high values for Hubble's constant and agreed that the universe is not as old as previous estimates have suggested. Experts said that the larger the value of the constant, the younger the universe must be and the faster its rate of expansion.

The studies also share an "unwelcome" twist: The oldest stars and galaxies in the universe are, by the best estimates, about 16 billion years old. So how can the universe be younger than that? Astronomers use a separate gauge, based on their understanding of thermonuclear reactions and stellar evolution, to judge the age of individual galaxies and stars.

"So we have a problem," acknowledged Pierce. "Either we are missing something in our understanding of the evolution and the age of the oldest stars or we are missing something in our understanding of how the universe has been evolving since the Big Bang.

"It is going to be very interesting in the next few years while we struggle to unravel this mystery," he said.

Kirshner agreed. "Both of us are in conflict with our understanding of the ages of the stars," he said. "Maybe the expansion of the universe has perhaps not been so simple."

Experts said the apparent paradox can be explained in one of three ways: The Hubble calculations simply may be wrong. The estimates of the age of stars and galaxies may be wrong. Or the conventional understanding of how the universe has evolved since its beginnings in a cataclysmic Big Bang may be wrong.

"No one understands by any simple means how the universe can be younger than the oldest objects we see around us," Maran said. "My personal opinion is that there is a basic property of the universe that has not yet occurred to us."

The Indiana team used three rare flickering stars called cepheids, which vary in brightness on a regular timetable, to calibrate the distance to the Virgo Cluster directly for the first time.

The astronomers focused on Virgo because that cluster of galaxies has been used by many researchers to gauge the relative distance between other celestial objects, even before any precise measure of its distance from Earth was available.

Using the Canada-France-Hawaii telescope on Mauna Kea in Hawaii, they determined that the distance to Virgo Cluster from Earth is 50 million light-years. Because the stars are twice as far away as the most distant cepheids previously studied, the team was able to calculate Hubble's constant with unusual precision.

In contrast, Kirshner's team used geometric measurements of five supernovas to derive an accurate measuring scale for the vast emptiness that separates galaxies.

The farthest exploding stars were more than 500 million light-years from Earth, but so bright that the supernovas were a million times brighter to observers on Earth than the cepheid stars in Virgo.

To calculate the distance to the exploding star, the researchers used its color and brightness as measured on Earth, combined with the velocity of the expanding gases from the heart of the mammoth thermonuclear explosion.

To make the proper measurements, astronomers must monitor the supernova in the first few weeks after the star explodes, before its superheated atmosphere has a chance to cool and become transparent. The new explosions enabled them to derive the new calculations.

Rethinking The Age of The Universe

Astronomers announced Wednesday that the universe is billions of years younger than previously estimated.

* The Question: How long has it been since the Big Bang, the primeval fireball in which time and space began?

* The Method: Any calculation of the universe's age depends on a measure of the speed at which the universe is expanding, called Hubble's constant. That in turn requires the separate measurement of the distance to galaxies.

* What They Did: An Indiana University group used more precise measurements of the distance to a cluster of galaxies called Virgo, shown above, while Harvard University group used huge exploding stars called supernovas--such as 1987A, shown below--as surveyor's marks.

* What They Found: The Indiana group said the universe could be as little as 7 billion years old; the Harvard group arrived at an age of between 9 billion and 14 billion years.

* The Problem: Since the oldest stars are more than 16 billion years old, how can the universe be younger than the things it contains?

* Things to Explore: The calculation could be wrong, the age of the stars could be off or theire is a hither-to-known property of the universe at work.

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