MIT physicists had close ties with laureate Giacconi


Riccardo Giacconi, a founding father of X-ray astronomy and co-recipient of the 2002 Nobel Prize in physics, had personal connections with many MIT X-ray astronomers in the 1960s and '70s, most notably his mentor, MIT's Bruno Rossi (1905-1993).

Giacconi, president of Associated Universities, Inc., and a research professor at Johns Hopkins University, shared the award earlier this month "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources."

Giacconi used X-ray detectors launched on a sounding rocket to discover the first cosmic X-ray source in 1962, finding that the universe contains a background radiation of X-rays. He was joined in this epochal discovery by MIT's Bruno Rossi, a pioneer in cosmic ray studies and later in X-ray astronomy and interplanetary plasmas. It was Rossi who first suggested that the search for celestial X-rays be carried out.

The Royal Swedish Academy of Sciences, in a background paper on the Nobel award, cited Herbert Friedman of the U.S. Naval Research Laboratory, Giacconi and Rossi as pioneers in X-ray astronomy, which they said began in 1949 with Friedman's discovery of X-rays from the sun.

"The most important leading persons through the first three decades of X-ray astronomy were, independently, Friedman and Giacconi. Also Rossi played a very important role, not the least as a senior colleague and mentor for Giacconi. These three persons contributed crucially to the development of methods and instrumentation, but also to the application of these methods to scientific work, leading to a very rich host of important discoveries," the Academy paper said.

"In a pioneering paper, Giacconi and Rossi (1960) discussed the possibilities of constructing imaging X-ray telescopes, inspired by earlier work on X-ray microscope design," the academy said.

In 1965, Giacconi obtained the first picture of the sun with an X-ray telescope that focused X-rays by means of grazing-incidence imaging optics. This proved that X-ray astronomy could photograph the sky just as do optical and radio astronomers do.

This event occurred after Giacconi started working in 1959 for American Science and Engineering Corp. (AS&E), a private research firm in Cambridge that was located on the site of MIT's current medical center. Although Giacconi did not have any formal connection to MIT, AS&E was founded in part by Martin Annis, a former Ph.D. student of Rossi. Rossi was chairman of the board and chief science adviser to the company.

"Our relations with Giacconi and his groups at AS&E and Harvard were extensive, intensive and rich while he was in Cambridge," said Hale Bradt, professor emeritus of physics at MIT. "It was no accident that he accomplished what he did. He was extremely talented, smart, decisive when necessary and able to see the big picture scientifically. He could be very persuasive and also very persistent in getting the resources from NASA that were needed to make successful his satellite programs."

To investigate cosmic X-ray radiation, which is absorbed by the Earth's atmo-sphere, you need instruments high in the atmosphere or in space. George W. Clark, professor emeritus of physics, and Minoru Oda, a Japanese scientist then at MIT, collaborated in subsequent AS&E rocket flights with Giacconi and his colleagues. One flight, in which Bradt participated, located the X-ray source called Sco X-1 with sufficient precision for it to be identified optically. This made possible ground-based studies by optical astronomers of these then mysterious sources.

MIT'S PROGRAM

Within a few years, MIT developed its own program of X-ray astronomy under Clark. He was joined in a high-altitude balloon program by physics professor Walter Lewin and, later, senior research scientist George Ricker. A sounding rocket program was begun in 1966 under Bradt and physics professor Saul Rappaport. The group was later joined by physics professor Claude R. Canizares. Under Clark's leadership, the group flew an experiment on the Orbiting Solar Observatory 7, which was launched in 1971.

In 1970, Giacconi's group launched the first satellite, named Uhuru, dedicated totally to X-ray astronomy. This allowed continuous observations of X-ray sources rather than the brief studies possible from rockets and balloons. This was a major step forward in X-ray astronomy's observational capability.

With the Uhuru observatory, several hundred X-ray sources were discovered. The observations demonstrated conclusively that X-ray sources can be binary star systems with a very compact object such as a neutron star, or a black hole in orbit with a more normal star, which transfers matter onto the compact object. As the matter falls towards the compact object, it gains a very high speed that drives its temperature up to millions of degrees. At such high temperatures, X-rays are emitted.

The MIT group in 1975 flew a follow-up satellite called Small Astronomy Satellite, again under Clark's leadership. It made its own important discoveries, in particular in experiments carried out by Lewin on the newly discovered phenomenon of X-ray bursts. MIT physics professor Paul C. Joss showed that these are thermonuclear explosions of the matter that has accumulated on the surface of a neutron star in a binary system.

Giacconi worked at the Smithsonian Astrophysical Observatory during the 1970s and was a professor in Harvard's astronomy department and associate director at the Harvard-Smithsonian Center for Astrophysics (CfA).

In 1977, the High-Energy Astronomy Observatory mission was launched. It carried two MIT experiments, one led by Lewin in collaboration with the University of San Diego and the other by Bradt in collaboration with Herbert Gursky of Giacconi's group. "The two groups [Smithsonian Astrophysical Observatory and MIT] worked as one; institutional affiliations were unimportant," Bradt said. Both experiments yielded additional valuable results.

Giacconi's dream of launching a large focusing X-ray telescope to study celestial X-ray sources came to fruition in 1978 with the launch of the Einstein satellite. The Einstein Observatory was the first fully imaging space-based X-ray telescope used for celestial (nonsolar) astronomy.

One of the Einstein instruments was the Focal Plane Crystal Spectrometer, developed in the MIT Center for Space Research under the direction of Canizares and Clark. This spectrometer made the first high-resolution measurements of cosmic sources.

Giacconi and colleagues submitted a proposal to NASA to initiate the study and design of an even larger X-ray telescope. After Giacconi left to become the first director of the Space Telescope Science Institute, the CfA group under the leadership of MIT Ph.D. graduate Harvey Tananbaum carried forward the program, culminating in the launch in 1999 of the Chandra X-ray Observatory, which is still operating.

MIT provided half the scientific instrumentation for Chandra and works with CfA to operate the mission, one provided by Ricker and the other by Canizares, now MIT's associate provost. "I met Riccardo the very first day I came to MIT, and he has remained the giant in the field since the beginning," said Canizares. "He has an outstanding combination of talents: as a visionary scientist, in instrumentation, in management of large projects and as an inspirational leader."

At present, MIT has two other X-ray astronomy experiments in space: one on the Rossi X-ray Timing Explorer under Alan Levine, principal research scientist, and the High Energy Transient Explorer under Ricker. The CfA and MIT groups look forward to more powerful X-ray missions in the future.

"MIT X-ray astronomers have had a close and mutually beneficial relationship with AS&E during Giacconi's time there and ever since with the Harvard X-ray group," Clark said.

Giacconi shared the 2002 Nobel in physics with Raymond Davis Jr. of the University of Pennsylvania and Masatoshi Koshiba of the University of Tokyo for their work in neutrino astrophysics.

A version of this article appeared in MIT Tech Talk on October 23, 2002.


Topics: Physics, Nobel Prizes

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