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Mark Shwartz, News Service (650) 723-9296, ; or Jenifer Conan-Tice,
Physics Department (650) 723-4347,

A chance to see our vibrant universe

It's an awesome sight: sudden, bright flashes from random directions in the night sky, jets of gas traveling at light speed across galaxies and neutron stars sending out beams of light. Our universe is vibrant and alive. And now's your chance to see it.

In a public lecture titled "New Views of a Vibrant Universe," Isabelle Grenier will present images of what the sky would look like if we could see X-rays and gamma-rays. Using colorful photos, movies and animations that translate gamma- and X-ray wavelengths into visible objects, Grenier will show us the true night sky -- one that will surprise even experienced stargazers. As she will explain, this high-energy view of the sky is changing our understanding of the universe.

Grenier, professor of astroparticle physics at the University of Paris and research scientist at the Commissariat a l'Energie Atomique/Departement d'Astrophysique, Saclay, France, will give the 2001 Hofstadter lecture at 8 p.m. Monday, March 12, in the SEQ Teaching Center, Room 201. She also will give a somewhat more technical talk March 13 at 4:15 p.m. in the same location.

The lectures were established to honor Nobel Prize-winning physicist Robert Hofstadter, who served on the physics faculty from 1950 until his death in 1990. Hofstadter was a designer of the Energetic Gamma-Ray Telescope that is largely responsible for the observations Grenier will describe.

"Aristotle said the sky was eternal and would not change. We now know that it's quite untrue," Grenier says. "As human beings, we have a view of the sky that is fairly static: The stars rotate and change with the seasons. If you look at high-energy gamma-rays, it's more like a Christmas tree with stars or the heart of galaxies flashing all the time. It's much more lively."

Here on Earth, we have no idea what we've been missing, and if it weren't for satellite telescopes designed to see high-energy particles, we'd still be in the dark. About once a day, bright explosions of gamma-rays light up the sky, but they are only seen by gamma-ray detectors in outer space. Our atmosphere absorbs them. The energy involved is truly enormous. "It's as if our sun converted all of its energy to gamma-rays in one second. That's how intense the radiation is," says Stanford physics Professor Peter Michelson.

Michelson, who is chair of the Hofstadter Lecture committee, says Grenier has a strong reputation in the international community for her work with exotic astrophysical sources of gamma-rays. "She's also a fantastic speaker who communicates the excitement of the field," he adds.

Michelson and Grenier collaborate on the Gamma-Ray Large Area Space Telescope (GLAST), which will go into orbit in 2005 to observe gamma-ray phenomena previously unseen.

In her afternoon talk on March 13, Grenier will describe clues to identifying 160 gamma-ray sources seen by the Compton Gamma-Ray Observatory (CGRO) and its predecessors during the last 30 years. "It's one of the objectives of GLAST to discover what these sources in the sky are," she says. Some may be in our backyard, in the unusual starburst region where the sun lies today. Others may be near the edge of the visible universe.

We tend to think of the universe as evolving over a long time. But gamma-rays and X-rays show things happening on much smaller time scales -- as short as seconds. "I don't think people have much of a flavor for that rapid evolution," she says. "The high-energy sky is the best way to feel it."


By Katharine Miller

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