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The newspaper of The Johns Hopkins University July 23, 2007 | Vol. 36 No. 40
Adam Riess of KSAS, dark energy discovery leader, shares Gruber Prize


By Lisa De Nike

Johns Hopkins astrophysicist Adam Riess, who led the first study revealing the existence of a mysterious "dark energy" permeating the universe, will share one of the most prestigious prizes in cosmology, it was announced last week.

The Peter Gruber Foundation said that its 2007 Cosmology Prize — a gold medal and $500,000 — will be presented to two teams of astrophysicists, the High-z Supernova Search Team and the Supernova Cosmology Project.

Riess, a professor in the Henry A. Rowland Department of Physics and Astronomy in the Krieger School of Arts and Sciences, is a member of the High-z team. He led the study for which High-z is being recognized, the first to show that a previously unknown force, now called "dark energy," is driving the universe to expand at an ever-increasing rate. The study was published in Astrophysical Journal in September 1998.

This is the second year that a Johns Hopkins astrophysicist has shared the Gruber Prize. Charles L. Bennett, a professor in Physics and Astronomy, was one of the leaders of the 18-member Cosmic Background Explorer team, which won the Gruber last year. The COBE satellite was developed by NASA's Goddard Space Flight Center to measure the early universe's now-diffuse infrared and microwave radiation.

Both of this year's teams are being honored for discoveries involving "dark energy," which is still not explained. Riess and High-z SN overall leader Brian Schmidt collaborated with other members of the team on the highly difficult and precise measurements — across 7 billion light-years — that led to the 1998 discovery.

"Our aim was to use supernovae — a special kind of exploding star — to measure how fast the universe was expanding in the past and then to compare it with how fast it is expanding now," Riess said.

The team anticipated finding that gravity — the attractive force that holds things together — had slowed the universe's rate of expansion over time. Instead, the astronomers were startled to discern that the rate of expansion is actually accelerating.

"If you tossed a ball into the air and it kept right on going up instead of falling to the ground, you would undoubtedly be very surprised. Well, that's about how surprised we were with this result," said Riess, who also is a scientist at the Space Telescope Science Institute, located on the Homewood campus.

Those observations sent the team back to the idea — first conceived by Albert Einstein but later rejected as his "biggest blunder" — that the so-called vacuum of space might produce a sort of "anti-gravity" energy that could act repulsively and would accelerate the expansion of the universe. Suddenly, that idea made sense.

Riess and other experts in the field refer to the phenomenon as "dark energy" and posit that it may account for up to 70 percent of the universe, "even though," he confesses, "we still don't understand it well at all."

Subsequent Hubble Space Telescope observations by Riess and the High-z SN team helped confirm the initial result in 2004. Riess, Schmidt and Supernova Cosmology Project leader Saul Perlmutter shared the prestigious $1 million Shaw Prize last year for this body of work.

Riess is a 1992 graduate of MIT, with a major in physics and a minor in history, and earned his doctorate in astrophysics from Harvard University in 1996. From 1996 to 1999, during which time the initial discovery was made, he was a Miller Fellow at the University of California, Berkeley. He has been an astronomer with the Space Telescope Science Institute since 1999 and joined the faculty at Johns Hopkins in 2006.

The two competing teams and their leaders — the High-z SN team, with Schmidt of the Mount Stromlo Observatory of the Australian National University in Canberra, and the Supernova Cosmology Project, with Perlmutter of the Lawrence Berkeley Laboratory at the University of California, Berkeley — will receive the Gruber Prize at a ceremony on Sept. 7 in Cambridge, England.

The annual Peter Gruber Foundation Cosmology Prize recognizes fundamental advances in research on the origin, development and structure of the universe. Co-sponsored by the International Astronomical Union, the prize aims to acknowledge and encourage further exploration in a field that shapes the way we perceive and comprehend the universe.


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