Expansion of universe once sluggish, now speeding up
Posted: October 10, 2003

Exploding stars, called supernovae, that are three-quarters of the way across the universe have helped astrophysicists discover that the universe has expanded at different rates over its cosmic history, reports Adam Riess from the Space Telescope Science Institute in Baltimore and a member of the Hubble Higher-z Supernova Search Team. He announced Friday, October 10, during the first-day of the Kavli-CERCA Future of Cosmology conference at Case Western Reserve University that approximately five billion years ago the universe began to accelerate in its expansion.

These new findings derived from images captured by the Hubble Space Telescope. Riess was among 70 of the world's leading researchers at the Kavli-CERCA (Center for Education and Research in Cosmology and Astrophysics) Future of Cosmology conference to explore the science of the universe, to report new information and to discuss the next 25 years of research.

"These Supernovae confirm past cosmic slowdown and the reality of recent cosmic acceleration or dark energy," states Riess.

"With Supernovae, we have mapped the preceding 75 percent of the expansion history of the universe," reported Riess.

Using the Hubble Space Telescope, the research group found six of the seven most distant Supernovae known and beyond the transition point between its slowdown and acceleration.

The Hubble Higher-z Supernova Search Team looked at a particular class of Supernovae known as Type 1a that are bright enough at ~10 billion solar luminosities at their peak light to be seen halfway across the visible universe from the ground and even further back in time with the Hubble Space Telescope.

While the previous slowdown was predicted by theory, Riess says actually seeing it "represents a crucial test of the new cosmological paradigm, which is now well-confirmed."

Five years ago, Riess and the High-z Supernova Search Team reported findings that the universe was speeding up in its expansion, which ran counter to what was expectednamely that the attractive gravity of dark matter would slow the expansion of the universe.

He further explains that gaining favor over the past years is the theoretical explanation that the universe is also filled with a repulsive dark energy.

Others on the Hubble Higher-z Supernova Search Team, under the direction of Riess, are Lou Strogler, Peter Challis, John Tonry, Stefano Casertano, Alex Filippenko, Robert Kishner, Widong Li, Saurabh Jha, Chuck Steidel, Mark Dickenson and the Goods Team under the direction of Mauro Giavalisco.

CERCA is a new center, designed to enhance the world-class research programs in cosmology and astrophysics already at Case by providing fellowships to enable some of the world's best young researchers to spend time at the University. The new center will come under the direction of Lawrence Krauss, Case chair and Ambrose Swasey Professor of Physics and the author of the best-selling book, The Physics of Star Trek. CERCA will involve a partnership between Case and its University Circle neighbor, the Shafran Planetarium at the Cleveland Museum of History, to design popular planetarium programs and ultimately documentaries and films that inform the general public about the latest developments in cosmology and astrophysics, says Krauss, adding that programs developed for the Shafran Planetarium eventually could be used by other planetariums around the country.

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