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MIT X-ray cameras probe universe

X-ray cameras designed by MIT researchers are aboard a satellite launched last week in Japan that could help scientists answer questions concerning the fate of the universe.

The satellite, an advanced astronomy observatory called the Astro-D, was launched at 11am Saturday, Feb. 20 (Japan time), on a Japanese rocket in a joint Japan-US endeavor. The launch occurred at Japan's Kagoshima Space Center on Kyushu.

Dr. George R. Ricker, a senior research scientist at the Center for Space Research, is the principal investigator for the US portion of the project. He said the launch "marked the culmination of five years of cooperative research and development by our group, working under the sponsorship of the NASA Office of Space Science and Applications, in collaboration with Japan's Institute for Space and Astronautical Science." The launch, he said, was the beginning "of a four-to-five year period of X-ray astronomy research in which MIT will be a full partner in continuing scientific investigations with our Japanese colleagues."

After it reached orbit, Japanese space scientists renamed the space observatory the Advanced Satellite for Cosmology and Astrophysics (ASCA). The acronym takes the same pronunciation as the Japanese word Asuka, meaning Flying Bird, and the satellite is also known by that name, Dr. Ricker said.

The MIT cameras are a breakthrough in solid-state X-ray sensors. They incorporate charge-coupled devices-made at MIT's Lincoln Laboratory- that make them so sensitive that for the first time scientists will be able to make pictures, and at the same time measure the energy, of individual X-ray photons.

The images should allow scientists to make much more sensitive observations over a broader band of frequencies than has been previously possible in X-rays.

"We have an opportunity to look back to where we are seeing the first generation of stars," Dr. Ricker said in an article in the New York Times by Andrew Pollack.

As a result, scientists are hopeful that data sent back from the Astro-D will help them answer critical questions about the early stages of the universe.

"Astro-D will be primarily oriented to looking at stars, stellar remnants, galaxies, clusters of galaxies, and quasars," Dr. Ricker said in a Tech Talk interview, "but we're also trying to use it to understand if there is material present in space that is non-luminous-in other words, dark matter."

Such dark matter could be key to whether the universe will continue expanding, or whether the process will halt. Theorists believe that this matter, while invisible, has a significant gravitational force that could one day stop the expansion.

This January scientists announced that the Roentgen Satellite (ROSAT), operated by Germany, Britain and the United States, had indicated that dark matter exists in a sufficient quantity to slow, and ultimately stop the expansion of the universe. Specifically, data from that satellite allowed the scientists to infer the presence of a tremendous amount of invisible matter around a cluster of three galaxies.

Data from the Astro-D could confirm the ROSAT findings, then tell whether that matter is an anomaly in the universe, or whether it occurs elsewhere. If the phenomena is found to be widespread, scientists could conclude that the universe will one day stop expanding.

Astro-D will be in orbit for four to five years. It will be followed by an even more ambitious satellite for X-ray astronomy, the US Advanced X-ray Astrophysics Facility (AXAF). MIT researchers from Dr. Ricker's research group and from a group headed by Professor Claude R. Canizares, director of the Center for Space Research, are responsible for instruments on AXAF, which is slated to be launched in 1998.

The MIT work on the Astro-D was funded by NASA.

A version of this article appeared in the February 24, 1993 issue of MIT Tech Talk (Volume 37, Number 23).

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