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The CfA Almanac Vol. XIII No. 2, July 2000
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CHANDRA OBSERVATORY WINS DISCOVER MAGAZINE AWARD

The Chandra X-ray Observatory, NASA's powerful X-ray space telescope and the third in its "Great Observatories" series, has been named winner of the Discover Magazine Editor's Choice 2000 Award for Technological Innovation.

The team of government, industry, university, and research institutions that designed, built and deployed Chandra were formally recognized June 24 in a ceremony at Disney's Epcot Center in Orlando, FL. Harvey Tananbaum, director of SAO's Chandra X-ray Science Center, which operates the spacecraft and its scientific observations for NASA, received the award on behalf of the team.

"Chandra has opened a new window for astronomers onto the universe of high-energy cosmic events such as pulsars, supernova remnants, and black holes," said Tananbaum. "We're now able to see spectacularly detailed images of celestial phenomena whose mere existence we could only imagine before."

Named in honor of the late Nobel laureate Subrahmanyan Chandrasekhar, the observatory was launched in July 1999 aboard the Space Shuttle Columbia and deployed to a highly elliptical Earth orbit. It uses an X-ray telescope with special mirrors designed by SAO's Leon Van Speybroeck to probe the mysteries of a universe that cannot be seen by conventional optical telescopes.

Among Chandra's most significant discoveries to date have been the detection of a giant ring around the heart of the Crab Nebula, details of the shock wave created by an exploding star, and resolution of the high energy X-ray "glow" in the universe into millions of individual light sources.

The Discover Magazine Awards for Technological Innovation, now in their 11th year, are designed to acknowledge the creativity of men, women, corporations and institutions who have reached superior levels of ingenuity. Chandra, and the other 2000 award winners, were listed in the July issue of the magazine.

COSMIC GAMMA-RAY BACKGROUND RADIATION MAY BE REMNANT OF LARGE-SCALE STRUCTURE FORMATION

The faint veil of gamma rays draped over the entire sky--long a puzzle for astronomical theorists--may actually be leftover energy from the cosmic construction project that created the large-scale structure in the Universe.

Massive shock waves, triggered by gravity during the formation of large-scale structures, such as the observed sheets and filaments of galaxies, were sufficiently powerful to produce today's observed background radiation, according to a model proposed by Abraham Loeb of the CfA and Eli Waxman of Israel's Weizmann Institute.

In an article in the May 11 edition of Nature, Loeb and Waxman suggest that the gravity-induced shock waves generated a population of highly-relativistic electrons, which, in turn, scattered the equally pervasive microwave background, itself a remnant of the Big Bang, pumping up a fraction of the microwave photons to gamma-ray energies, thus producing the all-sky gamma-ray background seen in today's universe.

The origin of the diffuse and pervasive background of gamma-ray radiation has been one of the great unsolved mysteries in cosmology. Even the known population of powerful extragalactic gamma-ray sources, called "blazars," can account for no more than a quarter of the gamma-ray background flux.

As recent results from the BOOMERANG experiment confirm, the Universe started from a nearly smooth initial state, but small density fluctuations in cosmic matter grew larger over time due to the effects of gravity. As the overdense regions condensed into large structures--such as filaments, sheets, and clusters of galaxies--the cosmic gas was shocked to a temperature of about ten million degrees.

These shock waves must have also produced relativistic electrons, say Loeb and Waxman, since x-ray and gamma-ray observations by modern telescopes have demonstrated the existence of such electrons in similar shock waves surrounding supernova remnants. Assuming that the physics of shock acceleration can be scaled up to intergalactic distances, Loeb and Waxman argue that similar high-energy electrons were produced in the intergalactic medium.

In the Loeb-Waxman model, the gamma-ray background was created primarily in those regions where dense filaments and sheets channeled gas from converging flows in the intergalactic medium. The hottest, most powerful shocks occurred at the intersections of these filaments, especially where they encompassed emerging clusters of galaxies.

Although rich young clusters are rare and make up only a fraction of the overall background radiation, they probably contain the strongest shock waves, say Loeb and Waxman, and thus should produce the strongest fluctuations in the diffuse background.

Direct detection of such shock waves would be the best way to test the model, say Loeb and Waxman. The first step, however, is to measure the smoothness of the background radiation on the sky with much greater precision. Although the level of precision needed is beyond the capabilities of existing telescopes, it will easily become accessible with the future Gamma-Ray Large-Area Space Telescope (GLAST), which is planned for launch in the year 2005.

conference gathering
Gathering after the first Sackler Conference's first session were, from left, Harvard Astronomy Department chair Ramesh Narayan, Princeton's Jerry Ostriker, keynote speaker and Astronomer Royal of England Martin Rees, conference organizer Avi Loeb, CfA director Irwin Shapiro, and sponsor Raymond Sackler. (Photo by Jim Cornell)

FIRST SACKLER CONFERENCE ON THEORETICAL ASTROPHYSICS HELD

The origin and early evolution of almost everything in the Universe was the all-encompassing subject of an extraordinary conference attracting several dozen of the world's leading astrophysical theorists to the Harvard-Smithsonian Center for Astrophysics this spring. "The First Generation of Cosmic Structures," held in Cambridge, MA, from May 15 through May 18, was the first in a new series of biennial conferences on theoretical astrophysics made possible through the generosity of Raymond and Beverly Sackler.

Weinberg, Shapiro, and Loeb
Nobel laureate and former CfAer Steven Weinberg (now of the University of Texas) presented the post-banquet talk for the first Sackler conference on Theoretical Astrophysics. Here, Weinberg (left) pauses to pose with CfA director Irwin Shapiro (center) and conference organizer Avi Loeb. (Photo by Mark Halevi)

conference break
The discussion of the origins of large-scale structures continued in the courtyard of Harvard's Chronkite Center during conference breaks. (Photo by Jim Cornell)

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