Radio Astronomy

Some of the earliest research in radio astronomy focused on the structure of our galaxy, the Milky Way Galaxy. Studying our own galaxy with light waves is extraordinarily difficult because our solar system is buried within the galaxy, and much of the light emitted by stars that make up the galaxy is blocked out by interstellar dust and gas.

Radio astronomy is better able to solve this problem because radio waves can travel through intervening dust and gas and provide images of the structures of which the galaxy is made. Of special importance in such studies is a particular line in the radio spectrum, the 8-inch (21-cm) line emitted by hydrogen atoms. When hydrogen atoms are excited, they emit energy with characteristic wavelengths in both the visual and the radio regions of the electromagnetic spectrum. The most intense of these lines in the radio region is the 8-inch (21-cm) line. Since hydrogen is by far the most abundant element in the universe, that line is widely used in the study of interstellar matter.

The 8-inch (21-cm) line can be used to measure the distribution of interstellar gas and dust within the galaxy. Since the galaxy is rotating around a common center, the motion of interstellar matter with respect to our own solar system (and consequently with respect to the galactic center) can often be determined. As a result of studies such as these, astronomers have concluded that the Milky Way probably has spiral arms, similar to those observed for other galaxies. One major difference, however, is that the spiral arms in our galaxy appear to be narrower and more numerous than those observed in other galaxies.

Radio emission from molecules in the interstellar gas provides radio astronomers with another important tool for probing the structure of our galaxy. Gases such as carbon monoxide (CO) emit at specific radio wavelengths, and are found in dark clouds of interstellar gas and dust. Because stars form in these regions, radio astronomy yields unique information on star births and on young stars.