An X-ray polarimeter, a powerful space instrument designed to study far-away sources of radiation and built by a collaboration headed by Columbia University's Robert Novick, is now expected to be lofted into orbit aboard a Russian satellite in late 1996.

In a joint announcement in Moscow on June 30, officials from the United States and Russia formally agreed that American space scientists will provide two instruments for the Spectrum-X-Gamma satellite mission.

Participants in the meeting, Daniel Goldin, Administrator of the National Aeronautics and Space Administration (NASA), and Yuri Koptev, Director General of the Russian Space Agency, signed a memorandum of understanding confirming U.S. participation in the Russian mission. The meeting was part of a series of discussions held in alternate capitals every six months between Vice President Al Gore and Prime Minister Viktor Chernomyrdin, as well as other cabinet-level officials, to discuss joint cooperation in a number of fields.

The instrument, titled the Stellar X-Ray Polarimeter, is being constructed by an international collaboration headed by Dr. Novick, professor emeritus of physics and special research scientist at Columbia. The collaboration also includes scientists and engineers from Lawrence Livermore National Laboratory,

NASA's Marshall Space Flight Center, Sandia National Laboratories and the Italian Consiglio Nazionale delle Richerche. Members of the Columbia team include Professor Novick; Philip Kaaret, associate professor of physics; and Joseph Dwyer, a postdoctoral research scientist.

The X-ray polarimeter will on launch be the only instrument in space capable of measuring the polarization of X-rays from astronomical objects such as neutron stars, black holes and supernova remnants, Professor Novick said. X-rays, like light, consist of wave-like pulses of energy, which can be polarized, or lined up in a certain plane. Measuring that polarization will give astronomers clues to certain astronomical events, such as whether an X-ray emitting region of space contains any black holes, objects so massive and dense that not even light can escape its gravitational field. They also hope to discover whether pulsars--dense, spinning stars also called neutron stars--emit X-rays in a fan shape or in a thin beam, and how radiation is emitted by other objects, such as quasars.

"The Stellar X-Ray Polarimeter will provide unique new information about what happens when matter falls into a black hole or onto a neutron star," said Dr. Kaaret. "Observations made with the polarimeter will lead to significant advances in our understanding of the physical processes occurring near neutron stars and black holes."

The project, begun in 1989, would have been impossible without the international collaboration, Dr. Kaaret said. Western scientists were unable to obtain space on any American space mission for the polarimeter, but the Russian space agency was able to provide the opportunity to fly a satellite-based instrument, he said, matching Western instrument-building skills with Russian satellite launching capabilities.

The X-ray polarimeter experiment is to be launched as part of a 2.5 ton scientific payload aboard a Proton rocket. The satellite will carry the most powerful X-ray and gamma-ray detectors ever orbited. A single orbit, with an apogee (maximum altitude) of 120,000 miles, about halfway to the moon, will take four days, allowing for unusually long observations of specific X-ray sources before the satellite swings behind the Earth.

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