SCIENTIST AT WORK: ADAM REISS
SCIENTIST AT WORK: ADAM REISS; His Prey: Dark Energy In the Cosmic Abyss
By DENNIS OVERBYE
Published: February 18, 2003
BALTIMORE— It was a quiet cloudy Saturday afternoon, and Dr. Adam Riess was more than a day into his search for a star.
Not just any star, but the galumphing galaxy-scorching explosion of a star giving way to age and gravity. These exploding stars, supernovae, can be seen across the universe. In them Dr. Riess can read the fate and nature of the universe.
Somewhere in the data on his computer screen, he hoped, was evidence of a star that had died before the Earth and Sun were born. He and his team had until Tuesday to find it.
But things were not going well. ''You know how nature likes to guard her secrets,'' he said, his voice trailing off.
He was dressed in a flannel shirt, baggy jeans and sneakers. On the wall over his computer hung a set of Dallas Cowboy bobble-head dolls. But his computer screen opened onto galaxies on the other side of the universe, stately kingdoms of stars, recorded by the Advanced Camera for Surveys on the Hubble Space Telescope and radioed to the Space Telescope Institute here.
Through Hubble's electronic gaze, these galaxies appeared as bits of indistinct fluff. But five years ago, as a member of one of two teams racing to divine the future of the universe, Dr. Riess used this type of data in a calculation that rocked astronomy. The expansion of the universe was speeding up under the influence of a mysterious antigravity, a ''dark energy'' embedded in space itself.
Since then, dark energy has prompted an outpouring of papers and speculations. The urgency of the supernova observations has been underscored by studies of radiation left over from the Big Bang, which suggest that dark energy constitutes some three-quarters of the weight of the universe. What is it? Where does it come from? Is it forever?
''It's so strange,'' Dr. Riess said. ''We have to be sure it's real.''
To find out, Dr. Riess and his colleagues have embarked on a search for the oldest supernovae they can find, stars whose light was traveling through the universe before dark energy made a mark on it. Clicking and pointing and running cursors over the flecks of light that Hubble sends to their computers, the researchers are looking for the one pixel out of a billion that is their exploding star.
That is the stargazing that appeals to Dr. Riess, who shares few of the classical astronomical virtues. He cannot identify the constellations. (''I can only find the Big Dipper,'' he admits.) He does not like to stay up late. ''I always regret it in the morning.''
Dr. Riess, the youngest of three children of an engineer and a psychologist, was born in Washington and raised in Warren, N.J. He studied physics at M.I.T. before taking up astronomy in graduate school at Harvard, where he studied with Dr. Robert P. Kirshner, an authority on supernovae.
Eventually, Dr. Riess became an expert in what he calls ''back end analysis'' of telescope data, particularly of exploding stars, work he continued as a postdoctoral student at Berkeley. Those analytic skills would be invaluable in the race to determine the fate of the universe.
For cosmology, the exploding stars of choice are known as Type Ia. They originate on dense burned-out cinders about the size of Earth that are known to astronomers as white dwarfs. Eventually, the Sun will end as a white dwarf, ever fading and cooling.
But if a white dwarf has a companion star, it can have a violent, brief resurrection as a Type Ia supernova. In that case, the intense gravity of the white dwarf can steal material from its neighbor. When its mass exceeds a critical limit, about 1.4 times the mass of the Sun, the star destroys itself in a fury as bright as four billion suns.
Because all Type Ia explosions start from the same point, astronomers have long hoped that their brightness is uniform enough to serve as ''standard candles.'' In other words, knowing how bright they actually are and how bright they appear to be through a telescope, scientists may be able to calculate how far away they are.
In the late 1980's a group of astronomers and physicists led by Dr. Saul Perlmutter, a physicist at the Lawrence Berkeley National Laboratory, began an ambitious effort to comb the cosmos for distant supernovae. Dr. Perlmutter was hoping to compare their distances to their speeds, to learn how fast the universe had been expanding since its creation in the Big Bang and how much it was slowing today, and thus whether everything would end one day in a ''big crunch.''
In 1996, another band of astronomers, including Dr. Riess and Dr. Kirshner, formed their own team to pursue the supernovae. The group, led by Dr. Brian Schmidt of the Mount Stromlo and Siding Spring Observatories in Australia, called itself the High-Z Supernova Search.
''We were the supernova pundits,'' said Dr. Riess. His contribution was to show how to correct for the fact that the Type Ia's were not quite as uniform as General Electric light bulbs after all. In 1992, Dr. Mark Phillips at the Cerro Tololo Interamerican Observatory in Chile, showed that brighter explosions faded more slowly than dimmer ones. By following the supernova's history, or ''light curve,'' astronomers could sharpen their estimates of its intrinsic brilliance and, thus, its distance.
Dr. Riess found a way to sharpen the estimates using the stars' colors. Brighter bursts were bluer than dimmer ones.