Molecules Between the Stars

Scientists once believed that the vast expanse between the stars was totally devoid of any kind of matter. But in the past few decades, they have been forced to change their minds. Besides confirming the presence of hydrogen and other earthly elements with optical and radio telescopes, astronomers have lately discovered a number of complex molecules in interstellar space: water, ammonia, formaldehyde and pairs of hydrogen and oxygen atoms that are ingredients of many other chemical combinations. Now the list has been further expanded. Researchers at the Bell Telephone Labs have detected large quantities of carbon monoxide in vast clouds of gas and dust in the Milky Way.

The study of interstellar matter--an emerging branch of astronomy called astrochemistry--is dependent on a fundamental property of molecules. When they are bombarded by radiation from the stars, they respond in a precise and predictable way: they radiate electromagnetic waves at characteristic frequencies. Detected by radio telescopes, these waves are the "fingerprints" that scientists use to identify interstellar molecules. Carbon-monoxide molecules, for example, radiate at an incredible 115 billion hertz (115 billion cycles per sec.).

Doubts Dispelled. Until recently, radio telescopes were not designed to pick up such high frequencies, but the Bell researchers--Arno Penzias, Robert Wilson and Keith Jefferts--had some timely aid: a newly developed telephone transmission device that can convert frequencies in the multibillion-hertz range into more easily detectable radio frequencies of about 100 million hertz. After adapting this device to the National Radio Astronomy Observatory's 36-ft. dish antenna at Arizona's Kitt Peak, the Bell scientists aimed the radio telescope at the distant Orion Nebula, a region of glowing gases more than 1,600 light-years away, a favorite target of molecule hunters.

There was an almost instant response. As Wilson glanced at the screen of a monitoring oscilloscope, he recalls, he saw "a bump that hadn't been there before." When the antenna was slightly moved, the bump disappeared. The scientists could scarcely believe their eyes. Though the equipment had just been switched on, it was already vigorously responding at 115 billion hertz--the fingerprint of carbon monoxide. The carbon-monoxide signals are, in fact, so strong, Jefferts says, that they almost "jump up and bite you." Any lingering doubts were totally dispelled in the next few nights. Shifting their telescope to other areas of the Milky Way, the astrochemists found at least ten galactic clouds that contain ordinary carbon monoxide; several of these were also found to contain isotopes of the gas. In addition, two clouds showed definite traces of cyanide, a combination of carbon and nitrogen that had already been detected optically far off in the Milky Way. "We made it look so easy," Penzias jokes, "that the bloom may soon be off the business of finding molecules in space."

Nebular Dust. Actually, that business has a promising future. Besides illuminating the complex mechanisms of stellar evolution and the building of elements, it could yield important clues to the origin of the universe. By measuring the effect on interstellar molecules of the so-called background radiation* (believed to be the faint remnant of the "big bang" that, according to one theory, created the universe), astronomers may learn more about the primordial explosion. Most intriguing of all, the molecules could provide tantalizing evidence of lifebuilding far from earth.

Until the discovery of complex interstellar molecules, astronomers were convinced that ultraviolet radiation and cosmic rays would quickly disintegrate any stray organic molecules that might form in deep space. Now they know that such molecules--which are essential to terrestrial life--can survive between the stars, apparently shielded by nebular dust. Indeed, Radio Astronomer David Buhl, one of those who found formaldehyde last year, thinks that organic molecules exist in considerable abundance in interstellar space. If so, he says, "life similar to ours" may well have evolved elsewhere among the 100 billion stars of the Milky Way.

* Discovered by Penzias and Wilson in 1965.

This file is automatically generated by a robot program, so reader's discretion is required.