April 1, 2002
Space exploration requires a great deal of imagination. With the international Space Very Long Baseline Interferometry mission, supported by NASA until last month, a global team of scientists and engineers not only imagined a telescope larger than Earth, they actually created it.
Black holes are perhaps the most elusive cosmic entity. Although we cannot see black holes, astronomers have confirmed their existence from the behavior of objects near the areas thought to be black holes. To learn more about these giant mysteries, scientists have to get a closer look at them. The very successful international joint mission has propelled astronomers one step closer to understanding the complex mechanisms that control black holes.
Although people generally think of black holes as all-consuming vacuums, they also eject material at speeds nearing the speed of light. The material emits radio waves, which can be detected by radio telescopes.
However, for a radio telescope to be able to observe details as fine as those observed by the Hubble Space Telescope, it has to be roughly 100,000 times larger than Hubble, or about 160 kilometers (100 miles) in diameter, said Dr. David Murphy, a JPL radio astronomer currently visiting the Japanese Space Agency.
To expand the resolution capabilities of ground radio telescopes, many radio telescopes can observe simultaneously to effectively "create" a telescope as big as the array of telescopes. However, even radio telescopes peppered across the globe aren't sufficient to see the necessary details around black holes. So a Japanese-built radio telescope in space was added to an array of 40 ground telescopes. The resulting "radio telescope" was as big as the orbit (32,000 kilometers or 20,000 miles). It revealed details in the observed objects more than 100 times finer than the Hubble Space Telescope can see. Sixteen different nations participated in the ambitious five-year mission.
"It was the United Nations of radio astronomy," said Dr. David Meier, a JPL astrophysicist. "To see different countries working together to build a single, very complex instrument was very impressive."
The project was "perhaps the most complicated science mission ever," according to project scientist Dr. Bob Preston of JPL.
The space telescopes relayed radio signals from the celestial sources to NASA's Deep Space Network, a set of communication antennas on three different continents, as well as to sites at the U.S. National Radio Astronomy Observatory and in Japan. These signals, along with those received at ground radio telescopes, were recorded on high-density videotape.
The videotapes were then sent to a common facility to be 'read' by a correlator that synchronizes tapes from every receiver to within one millionth of a second. With the help of computer software that mimics the focus of a camera, the radio waves become celestial images.
"It's like looking at a picture made with radio waves by a camera that's larger than Earth," said Dr. David Meier, JPL astrophysicist. "We are able to zoom into the centers of black holes closer than any other imaging technique."
In addition to many awe-inspiring pictures, scientists have gained extensive scientific information from the mission, with results appearing in more than 200 scientific papers. A lot has been learned at the most fundamental level about the environment near super-massive black holes. Material escaping in jets from black holes in the center of galaxies was confirmed to be moving nearly at the speed of light. The structure, time-variability and magnetic fields of material near the black holes provided additional clues to the nature of these violent regions of space.
The mission also concentrated its enormous magnification power on other energetic celestial objects, such as pulsars. A pulsar is a neutron star, an extremely dense object formed by a supernova explosion at the end of a massive star's lifetime. The mission also studied molecular masers in star-forming regions. A maser is a cousin of the laser that transmits a highly focused beam of microwave energy.
In the future, radio astronomy will become even more precise. If selected by NASA, the Advanced Radio Interferometry between Space and Earth mission will further the study of supermassive black holes by obtaining images with resolutions 3,000 times greater than NASA's Hubble Space Telescope.