Many celestial objects have temperatures too high to be seen in the visible range of light, but they emit energy levels that can be observed in the X-ray band. The Columbia researchers built an X-ray sensor so sensitive that it can look back halfway into the history of the universe and detect millions of X-ray sources.

Scientists will now be able to see how matter in the universe, usually gases from stars and dust, behaves when it gets pulled into the gravitational fields of very hot, high-density neutron stars and black holes -- objects that have been previously unobservable.

"The challenge was in the engineering design," said Steven Kahn, chair of Columbia's physics department. "We were designing something that was beyond state-of-the-art; so, we not only had to build it, we had to invent and create the tools we needed to build it."

Kahn, with his team of astrophysicists, including research scientists Frits Paerels and Andrew Rasmussen and graduate student Jean Cottam, received a $25-million grant from NASA and has spent 15 years to develop the X-ray technology needed for such a sensitive instrument.

The design is intricate, with 200 thin gold plates that must be positioned so accurately that shifts of even one micron will affect the instrument's ability to assign wavelengths and colors to the X-ray radiation detected in outer space.

"One of our concerns was that the turbulence from the rocket launch will shift the instrument," said Kahn. "But we designed titanium flexures around it to absorb any shaking, and that worked very well in all of our pre-launch trials."

The X-ray Multi-mirror Mission satellite, called XMM, is a consortium between many countries, including Britain and Switzerland, with Columbia University leading the American effort. It is one of four major missions of the European Space Agency (ESA), and will be launched in French Guiana, near the equator. The equatorial site is a requirement for the 48-hour orbit around the earth, which takes the satellite halfway to the moon.

In addition to Columbia's X-ray spectrometers, the satellite carries three X-ray imaging cameras and a 300mm-diameter optical monitoring telescope that will for the first time allow simultaneous observation of the visible and near-infrared wavelengths. The whole machine weighs almost four tons and its solar panel "wingspan" measures more than 30 feet.

After a period of calibration, XMM will begin sending data to ESA's Science Operations Centre in Villafranca, Spain in February 2000. Scientists expect it to gather information for 10 years, although all hope it will be even longer.

"It's amazing to be at the point we can collect quantitative data on things we know so little about," said Rasmussen, who will accompany Kahn and other team members to the launch in December. "We are actually going to be able to see the temperature, density and composition of the gases swirling around a black hole."

Near-Earth Satellite Will Measure Sun's Energy
A new satellite experiment, designed by Columbia scientist Richard C. Willson, will measure the total amount of sunlight reaching Earth that powers its climate and weather systems. To be launched on Dec. 19, it will continue NASA's effort to determine whether an increasing trend in solar radiation discovered by recent experiments is continuing and contributing to a rise in global temperatures.

Although the sun's 11-year radiation change during a solar cycle is fairly well understood, small changes in the sun's overall output may have a significant role in global warming and other climatic changes on both shorter and longer time scales.

These range from El Ninos and La Ninas, on time scales of about two years, to little ice ages, on time scales of about 200 years. The Active Cavity Radiometer Irradiance Monitor (ACRIM) measures the sun's total energy output over time with state-of-the-art precision and will provide climatologists with data to improve their climate models and ability to make predictions over the next century.

"Small, sustained changes in total solar output of as little as 0.25 percent per century could become the primary cause of significant climate change on time scales of many decades," said Richard Willson, the experiment's principal investigator, who is based at Columbia's Center for Climate Systems research in Coronado, Calif. "The information we receive from this will be critical to understanding Earth's present climate and the possibility of climatic changes and global warming in the long-term."

This project is the third in a series of ACRIM satellite experiments to monitor solar variability in order to understand the radiation that creates the winds, heats the land, and drives the ocean currents. Results from the first two, launched in 1980 and 1991, indicate a subtle upward trend in total solar irradiance over the two decades.

The ACRIM III instrument is the sole payload of a small, 253-pound ACRIMSAT satellite that will be launched into circular orbit 425 miles above Earth by a Taurus commercial launch vehicle on Dec. 19. It always points toward the sun, and takes only 98 minutes to travel around Earth once. NASA's Jet Propulsion Laboratory (JPL) Pasadena, CA, built the ACRIM III instrument to the specifications of Willson, who directs all science operations. Orbital Sciences Corporation (OSC) provided the ACRIMSAT satellite and Taurus launch vehicle under contract to JPL.

Co-investigators include James Hansen, director of NASA/Goddard Institute for Space Studies, Alexander Mordvinov, Institute of Solar Terrestrial Physics, Russian Academy of Sciences, and Hugh Hudson, University of Calif. at San Diego.

The total cost of the experiment, including the instrument, satellite, launch and five-year science mission is under $30 million. It will launch about two years after project startup and represents a new paradigm for small experiments in NASA's effort to maximize science return per tax dollar spent in their "better, faster, cheaper" research efforts.