Images of quasars billions of light-years away are among the striking initial results of the Very Long Base Interferometry (VLBI) Space Observatory Program, a new type of astronomy mission that uses a combination of satellite- and Earth-based radio antennas to create a telescope larger than Earth.
Initial results of the radio interferometry mission, launched in February 1997 by Japan's Institute of Space and Astronautical Science (ISAS), are reported in the September 18, 1998, issue of Science magazine.
NASA's Jet Propulsion Laboratory, Pasadena, CA, is part of an international consortium of organizations that support the mission, that creates the largest astronomical "instrument" ever built -- a radio telescope more than two-and-a-half times the diameter of the Earth. One of the most complex space missions ever attempted, Space VLBI has given astronomers one of their sharpest views yet of the universe.
The Science article releases four new images, all depicting quasars whose emissions are estimated to have traveled billions of years to reach Earth. "These images probe some of the most distant and ancient objects in the universe, giving us a glimpse of quasars as they existed billions of years ago," said co-author Dr. Robert Preston, project scientist for the mission at JPL. "These powerful objects exist at the center of many galaxies, including our own familiar Milky Way, which has a weak version of a quasar."
Key results detailed in the article revolve around images of extremely distant objects created through a combination of raw data from the space radio telescope and an array of ground radio telescopes, along with highly sophisticated digital imaging techniques. Of special note is the value of such images in clearly resolving individual components in the observed quasars' jets, which are composed of material rushing away from quasars at nearly the speed of light. The four quasar images are available at http://www.jpl.nasa.gov/releases/98/spacevlbi.html.
Quasars are enormously bright point-like optical objects, often shining with an intensity many hundreds of times that of an entire galaxy. It is believed that quasars are powered by gas and the remnants of stars spiraling into black holes that have masses of millions to billions of times that of our Sun. Black holes are objects that are so massive that no light or matter can escape from them. Some of the material rushing into the black hole is thought to be thrown away at enormous speeds to form the observed narrow, radio-emitting jets. By studying these jets, astronomers hope to learn more about the black holes that power them.
Very long baseline interferometry is a technique used by radio astronomers that electronically links widely separated radio telescopes together to form a single instrument with extraordinarily sharp "vision," or resolving power. The wider the distance between the telescopes, the greater the resolving power. In this first-ever dedicated mission of its kind, astronomers have approximately tripled the resolving power previously available with only ground-based telescopes. The Space VLBI satellite system has resolving power more than 100 times greater than the Hubble Space Telescope has at optical wavelengths. In fact, its resolving power is almost equivalent to being able to see a grain of rice in Tokyo from Los Angeles.
The project, a major international undertaking, is led by Japan's ISAS, backed by the National Astronomical Observatory of Japan. Collaborators include JPL; the National Science Foundation's National Radio Astronomy Observatory (NRAO); the Canadian Space Agency; the Australia Telescope National Facility; the European VLBI Network and the Joint Institute for Very Long Baseline Interferometry in Europe. More than 50 scientists associated with these and other collaborating institutions contributed to report published in Science magazine overview paper.
The Space VLBI project's eight meter (26-foot)-diameter orbiting radio telescope observes celestial radio sources in concert with a number of the world's ground-based radio telescopes. It is in an elliptical orbit, varying between 580 and 21,700 kilometers (360 and 13,484 miles) above the Earth's surface. This orbit provides a wide range of distances between the satellite and ground-based telescopes, which is important for producing a high-quality image of the radio source being observed. One orbit of the Earth takes about six hours.
Approximately 40 radio telescopes from more than 15 countries have committed time to co-observe with the satellite. These telescopes include NASA's Deep Space Network antennas in California, Spain, and Australia; the National Science Foundation's Very Long Baseline Array (VLBA), an array of 10 telescopes spanning the United States from Hawaii to Saint Croix; the European VLBI Network, more than a dozen telescopes ranging from the United Kingdom to China; a Southern Hemisphere array of telescopes stretching from eastern Australia to South Africa; and Japan's network of domestic radio telescopes.
JPL manages the U.S. Space Very Long Baseline Interferometry project for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology.
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