One cool, clear night last November a gleaming Atlas-Centaur rocket sat ready on its floodlit launch pad at Cape Kennedy. Perched atop the silver booster, the High Energy Astronomical Observatory-2 (HEAO-2), the most ambitious and advanced astrophysics research probe ever, lay shrouded in protective covering.
As midnight passed and the countdown approached zero, tension increased inside the lead-enclosed control room three miles from Ground Zero, and at the Harvard-Smithsonian Center for Astrophysics (CFA), where project scientists put aside their munchies and listened intently--by an audio hook-up.
Pat Henry, an associate of the Harvard College Observatory (HCO) who worked on a vital component ("it's analogous to an X-ray T.V. camera") of HEAO-2's sensitive X-ray telescope, decided he didn't want to watch the launch on a monitor.
"With about 30 seconds to go I ran outside of the control room," he remembers. "I wanted to see it with my own eyes, and hear it, too. It lifted off, and I watched it rise up over the fields.
Henry added, "I kept expecting to see it blow up, but it didn't." Far from it. Not only did HEAO-2 attain a nearly letter-perfect orbit, but in its first five months the X-ray observatory has returned a wealth of previously unobtainable photos and data, found a probable answer to one of the universe's most difficult questions and raised numerous new ones.
To backtrack a bit, though, twenty years ago, X-ray astronomy barely existed. Today it is at least as important as optical and radio astronomy in helping earthbound scientists study the skies.
X-rays, energetic particles which are emitted from a variety of celestial objects and travel at the speed of light (approximately 186,000 miles/sec.), cannot be detected on Earth because the atmosphere absorbs them before reaching the surface--thus the need to get into space to conduct X-ray observations.
Back in 1960, when the only known source of X-rays in space was the sun (though astronomers suspected they would find other sources if they had the equipment to look for them), Riccardo Giacconi, then with American Sciences & Engineering and now a professor of Astronomy here, first proposed a method for using telescopes to take detailed X-ray photographs of distant objects.
As Giacconi recalled last week, the problem entailed getting enough X-ray particles to fall on a detector and create an image, like light (in the form of "photons") hitting film in a camera. Giacconi saw that by positioning mirrors at shallow angles to the incoming radiation, astronomers could collect X-rays over a large area and funnel them onto a small detector, allowing for photographs "a millionfold" more detailed than previously possible.
The theory was there; but technology still needed time to catch up. "We realized that the technology would take many years to develop, but it was a great boost knowing that we ultimately knew a way to make X-ray astronomy very sensitive," Giacconi remembers. Before HEAO-2 could become a reality, though, X-ray astronomy would have to make sporadic progress. In 1962, a group headed by Giacconi discovered the first X-ray star; eight years later the same personnel were responsible for the first orbiting X-ray observatory (named "UHURU" after the Bantu word for freedom).
Though important advances resulted from these and other early missions, the results were still comparatively primitive--the best pre-HEAO-2 X-ray photos of the sky show only blurs and blotches. Though many different and powerful X-ray sources had been found-- among them the leftovers from stellar explosions ("supernova remnants"); some unusual galaxies; and quasars, star-like objects that gave off enormous amounts of energy--their precise structure still could not be observed.
HEAO-2, dubbed the "Einstein Observatory" in honor of the physicist who was born a century ago this year, would change all that. With an X-ray telescope a thousand times more sensitive than any previous instruments, Einstein for the first time has been able to take high resolution X-ray photographs and accurately measure the size, shape and structure of X-ray sources as far as the edge of the known Universe--more than 15 billion light-years away.
Although the $85 million dollar NASA-funded project has been directed by a consortium of four groups--CRA, MIT's Center for Space Research, Columbia University and the Goddard Space Flight Center in Maryland--the main impetus for the mission has come from 60 Garden St. Giacconi is the overall director of the Einstein Observatory, while scientific responsibility rests with Harvey Tannenbaum, an associate of the Harvard College Observatory.
As the November 13 launch approached, a good part of the Center for Astrophysics revved up for the mass influx of raw data that soon would be arriving. All observation plans for and information analysis from HEAO-2's 0.6-meter reflection X-ray telescope are coordinated from CRA. It took a week for the first picture to arrive on the monitors in Room 306-B. That shot was of Cygnus X-1, a radiation source which many astronomers believe is a black hole, a compressed star with gravity so strong that light cannot escape from it.
"Finding that first target was the neatest possible thing," Henry says. "It took about five minutes for Einstein to move into position, and sure enough we saw this X-ray source move into the center of the picture, stop in the middle of the screen and start building up.
"It was just fantastic to see those X-rays coming down the pipe," he adds.
And, especially after Einstein went into full operations on January 15, the X-rays really have been "coming down the pipe," and from a wide spectra of sources.
"We learn as much in astrophysics from two days from Einstein as we learned in the first