In 1932, a Bell Telephone Laboratories engineer named Karl Jansky was hunting down sources of radio static when he detected a persistent noise coming from one part of the sky. The source, as it turned out, was some cosmic unrest at the heart of the Milky Way. No optical telescope could see past impenetrable clouds of gas and dust. But Jansky's radio could hear what was happening.
Since then, astronomers have confirmed that the best way to learn about deep space is often to tune in to its hissy song. And hundreds of millions of dollars have been spent on ever-more-ambitious devices for doing so. For example, the radio telescope built in 1963 in Arecibo, Puerto Rico, stretches 1,000 feet across a small valley. With it, astronomers have listened to the rapid spinning of burned-out stellar corpses and discovered an improbable family of planets serenely circling one of them. The Japanese government recently launched a radio telescope into space itself, and next year nasa will loft another satellite to study the short-wavelength radio waves left over from the time of the Big Bang.
Still, no telescope inspires more awe than the Very Large Array, completed in 1980. Its 27 radio dishes, each 82 feet wide, stand in formation across the New Mexico desert like a set of abandoned alien spacecraft. A series of computers and electronic connections unites them into one huge telescope, 22 miles wide. The whole gargantuan herd, called the vla for short, lumbers along railroad tracks to form different patterns that adapt to scientists' needs.
The array can transform feeble radio signals into spectacular images. Unlike light waves, radio waves are long enough—about an inch to a yard for the images in this article—to leap right over bits of interstellar debris. And while light comes mostly from stars, radio waves emerge from many kinds of cosmic disturbances. Seen through a traditional telescope, light from the galaxy M87 shows little more than a fuzzy ellipse of stars. A new VLA image reveals twin jets of gas shooting from that galaxy's center, inflating a placenta of energized gas 200,000 light-years wide. The jets originate in a compact object at the galaxy's center, probably a black hole weighing as much as three billion suns.
Nearly every discovery is a surprise where this still-infant technology is concerned. Just recently, the Very Long Baseline Array—10 matched telescopes, linked together to form an instrument effectively 5,000 miles wide—baffled researchers with the news that the universe is smaller and younger than was previously thought. They'll just have to keep tuning in to see what comes next.
RADIO PIONEER By sweeping his rotating radio detector back and forth, Bell Labs engineer Karl Jansky identified the first deep-space radio signals.
A NEW VIEW Grote Reber, a radio engineer working in Illinois, built the world’s first true radio telescope in his spare time and by 1941 had completed a crude survey of the radio sky.
SUPERSTARS A supernova explosion created the tortured Crab Nebula in 1054. At the center is a dense, rapidly rotating stellar cinder that gives off radio flashes 30 times per second.
BRIGHT LIGHTS Quasars and radio galaxies, discovered by radio telescopes in the early 1960s, are the most consistently luminous objects known. They are probably powered by gas falling into a black hole.
THE BIG PICTURE The COBE satellite, launched in 1989, carried the study of microwaves into space and confirmed that the universe began in a hot fireball.
MANY MILKY WAYS Visible light is only one way to look at the universe. Each strip below shows the plane of our galaxy in a different part of the electromagnetic spectrum, revealing unique information. Radio continuum is from hot, electrically charged gas. Atomic hydrogen emission comes from warm gas. Molecular hydrogen lies in cold clouds, where stars form. Far-infrared rays highlight dust grains, while near infrared comes mostly from low-mass stars. Visible light is mostly from sunlike stars. Ultraviolet is heavily obscured by interstellar junk. X rays come from energized gas. Gamma rays appear where high-speed subatomic particles collide with interstellar hydrogen.
HEART OF THE GALAXY Radio waves captured by the Very Large Array unveil a dynamic scene at the center of the Milky Way. The prominent mass of agitated gas, known as Sagittarius A, marks the exact hub of our galaxy and may contain a massive black hole. Just above and to the left are nebulae full of hot, newborn stars. Round puffs are the remnants of supernova explosions that spew out oxygen, carbon, and nitrogen—the chemicals of life. The whole picture is about four degrees wide, or eight times the width of the full moon. An optical photograph of the same region shows none of these details because intervening clouds of gas and dust block the view.
CONSTRUCTIVE INTERFERENCE Radio telescopes need to be huge because radio waves are so much longer than light waves, but it is very difficult to build an antennae more than a few hundred feet across. So astronomers combine the signals from widely separated antennae to create, in effect, a single instrument as large as the distance between the two. This technique is known as interferometry. Radio waves arriving head-on reach the two antennae in step. If the waves are slightly off-axis, they’re out of step, so they partially or totally cancel each other. A computer then calculates the exact location of the source. Radio telescopes can be linked across continents, or with companion instruments in space, to create detectors thousands of miles wide. Such devices can provide images a hundred times sharper than those from the Hubble Space Telescope.
RADAR REVELATIONS Some radio telescopes, like Arecibo in Puerto Rico and Goldstone in California, send as well as receive radio waves. Radar signals from these instruments can produce meaningful maps of asteroids that look like mere dots of light in ordinary telescopes. This image shows the battered surface of a two-mile-wide asteroid, 1999JM8, as it recently raced by Earth.
TIME-LAPSE EXPLOSION In 1993 a star blew up in nearby galaxy M81, sending a shell of hot, radioactive gas speeding outward at thousands of miles per second. The tremendous resolving power of the Very Long Baseline Array allowed astronomers to watch as the irregular shell of gas expanded into the interstellar medium.
TWO-FACED GALAXY In a visible-light image, the giant galaxy M87 in the constellation Virgo looks fairly ordinary . Yard-long radio waves collected by the Very Large Array expose the galaxy’s hidden personality . A black hole at the center shoots out high-speed jets of charged subatomic particles, which expand until they hit infalling material from outside the galaxy. Widely separated, linked antennae produced zooms toward the inner region of the main jet .
MOBILE ARRAY The telescopes of the VLA can roll along their railroad tracks at about five miles per hour. Astronomers schedule their observations at the $80 million facility months or years in advance, depending on which antenna configuration they need to use.
ULTIMATE EXPLORERS The 1,000-foot Arecibo telescope, seen here during its recent upgrade, is the largest single-dish antenna in the world. It is fixed in the ground but can adjust its gaze slightly by moving a suspended, signal-collecting dome. Arecibo is used to search for signals from possible alien civilizations in addition to its more conventional astronomy work. The 330-foot Green Bank Telescope in West Virginia (left) will be the biggest fully steerable radio telescope when it is completed next year. Its unusual design eliminates the support structures that normally block part of the incoming radio waves.
PUSHING THE ENVELOPE The James Clerk Maxwell telescope atop Mauna Kea in Hawaii observes rays that are shorter than radio but longer than infrared. This little-explored region of the electromagnetic spectrum is a good place to observe planets forming around young stars or distant galaxies shrouded in dust.
RELATED WEB SITES: For a thorough introduction to radio astronomy on the Web, visit the National Radio Astronomy Observatory home page at www.nrao.edu/intro/.
The images of the Milky Way shown in different kinds of radiation come from a variety of sources. Most can be found on-line at adc.gsfc.nasa.gov/mw/milkyway.html. The ultraviolet image is courtesy the euve Project, Center for euv Astrophysics, University of California at Berkeley (www.cea.berkeley.edu/).