New Space Observatory To Probe Mysterious X-Rays In The Sky

October 26, 1996

A new space observatory built at Penn State and known as "CUBIC" will be launched into Earth orbit shortly after noon on Tuesday, October 29, 1996. Scientists expect the observatory to help them learn more about the unknown sources of a diffuse glow of X-rays reaching the Earth.

NASA will provide live television coverage of the launch, which will be aired at Penn State in 101 Thomas Building on the University Park Campus beginning with launch commentary at 11:00 a.m. EST. Seating is available for about one hundred people.

"If our eyes could detect X-rays, the night sky would look completely different," says David N. Burrows, associate professor of astronomy and astrophysics at Penn State and head of the team that built CUBIC. "Instead of seeing a black sky between the stars, we would see a bright glow in all directions, much like looking at the night sky in a city. We still know very little about this diffuse X-ray background that surrounds us," he says.

"We know the most energetic X-rays are produced by black holes far outside our galaxy and the least energetic ones are almost all coming from hot gas in our Milky Way galaxy within a few hundred light years of the Sun, but the X-rays at intermediate energies are a mystery," Burrows says. The researchers hope CUBIC will help them better understand the source of the diffuse X-ray background by providing detailed information about its energy spectrum.

CUBIC will be the first instrument in space specifically designed to look at the diffuse X-ray background with high-resolution devices known as CCD detectors, which convert X-rays into electronic signals. CCDs can measure the energies of the X-rays about 10 times better than earlier technologies. The CCD detectors in CUBIC are similar to the light detectors in modern home video cameras, but they are specifically designed to detect X-rays in space. "The X-ray CCDs in CUBIC will give us an image plus a higher-resolution energy spectrum than ever was possible before," Burrows says.

An X-ray is a high-energy photon--like visible light except it has much more energy. "The colors of the photons of light you see as your electric range heats up give you an idea of how hot the burner is, and if you could heat it high enough, its glow would change from black to red to white and would eventually go into the ultraviolet and then into the higher-energy range that produces X-rays," Burrows explains.

The mysterious X-rays CUBIC is designed to study are produced by extremely thin gas in space that is extremely hot. "We suspect this material is heated up to millions of degrees by supernova explosions," Burrows says. "But right now our theories can't really explain what is going on in this intermediate energy range, so we might even find a previously unknown source of energy within the Milky Way that is producing these X-rays," he says.

By studying the energy spectrum of the X-rays, scientists expect to learn more about the makeup of the hot gas that emitted them. "Analyzing the spectrum to find out how much carbon, oxygen, iron, and other elements are in the gas can tell us whether this gas came from supernova explosions, which produce many of these heavier elements," Burrows explains. He also expects to be able to tell whether the X-ray-emitting gas contains material clumped together in tiny dust grains or whether these dust grains have been blasted apart into individual ions by a supernova shock wave.

Burrows and his team of a dozen students, engineers, and technicians built CUBIC at Penn State using CCD detectors specially built for them by EEV, Inc. in New York in collaboration with scientists at the University of Leicester in England. "We built the camera that those detectors go into, the electronics that makes them work, the mechanical structure, and the support structure that cools the CCDs down, processes their signals, turns them into useful scientific data, and then transmits them to the ground," Burrows says. "The students, especially Jeff Mendenhall, Laura Cawley, Kaori Nishikida, and Catherine Grant, were involved in testing the detectors and in helping to calibrate the instrument."

Most of the data from CUBIC will be analyzed at Penn State during the next three to five years. "We have a big opportunity and also a big responsibility to make sure that it gets processed and analyzed properly and that we get everything squeezed out of it that we can," Burrows says. "We'll point CUBIC in one direction and collect data there for about four days--which will give us a very good spectrum--and then we will rotate the satellite and collect data for four days from a different target, which will give us about two good spectra per week for as long as the satellite keeps working."

Each day during its life, the satellite will pass four or five times over the ground station in Argentina and transmit its data, which the Penn State team will analyze from its CUBIC operations center at Penn State using an Internet connection to the ground station. "We have a computer down in Argentina that will be running our analysis software so we can keep an eye on the data to make sure everything is working," Burrows says. "Ten years ago we would have had to go to Argentina or wait until the data got mailed to us later, but now we can analyze a lot of it almost in real time across the Internet and if something is wrong we can get it fixed right away."

CUBIC is one of four instruments installed on the SAC-B satellite, an international cooperative project between Argentina's National Commission of Space Activities (CONAE) and the U. S. National Aeronautics and Space Administration (NASA). NASA coverage is available on Spacenet 2, Transponder 5, Channel 9, located at 69 degrees west longitude beginning at 10:00 a.m. with the rebroadcast of a press conference concerning the launch.

- B K K -Contact: Barbara K. Kennedy, 814-863-4682, e-mail:, for information on how to reach Dr. Burrows at the Wallops Island launch site or a photo of CUBIC.

More information on CUBIC is available on the World Wide Web at

Penn State

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