ALBUQUERQUE, N.M. - Herb Gursky remembers the first space mission designed to search the heavens for X-rays. It launched into Earth orbit in the fall of 1961. But some doors on the satellite failed to open and the onboard Geiger counter was rendered useless. Gursky and Frank Paolini worked under the direction of Riccardo Giacconi at American Science & Engineering, a company that supported the military's testing of nuclear weapons over the Pacific.
On June 12, 1962, these pioneering X-ray astronomers launched their Geiger counter again from the White Sands Missile Range 150 miles south of here. The mission's primary objective was to look for X-rays coming from the Moon. A secondary goal was to search the sky for other possible X-ray sources. Six days later, on June 18, the satellite had returned some 300 seconds of data that led to the discovery of the first X-ray source outside our solar system.
"It certainly was a surprise," Gursky told a group of reporters here at the 200th meeting of the American Astronomical Society earlier this month. "It wasn't an accident."
The X-ray source was named Scorpius X-1, because it was located in the constellation Scorpius. It was later determined to be a neutron star with an orbiting companion star that feeds it gas, which spirals inward, heats up, and generates X-rays.
In recounting the discovery, Gursky said the signal was so strong that a technician, Tom Quinn, exclaimed, "There it is," meaning the Moon.
"I was looking at the same data but knew that the signal was too strong to be fluorescence X-rays from the Moon," Gursky said. He considered that the source might have been caused by particles trapped in Earth's magnetic field. Eventually this and other possibilities were eliminated, leaving Scorpius X-1 as the source.
A year later, other researchers found that there were X-rays everywhere in space, a so-called "X-ray background radiation." In 1964, scientists observed the Crab Nebula as it was eclipsed by the Moon. Because X-ray detections fell off as the Crab disappeared, the researchers concluded that it was the source of the radiation.
Within a couple years, astronomers knew that much of the X-ray background was in fact generated by what they now call "point sources," individual stars and galaxies.
By the end of the 1960s, astronomers had discovered X-ray emitting, fast-spinning stars called radio pulsars, and they had detected the first quasar, which they later determined was a supermassive black hole anchoring a galaxy in the very distant and young universe.
"By 1970 astronomy was a different discipline than it was in 1960," Gursky said.
He attributes the advances to technology that was largely developed during World War II, from high-performance rockets to advance radio and radar technology.
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