Science: Galaxy’s Heart

Though relatively few earthlings are aware of it, they are embedded in a huge, disk-shaped spiral galaxy. Earth’s astronomers have a hard time seeing much else; every star visible in the sky is part of it.* They have an even harder time seeing into its heart (located roughly in the direction of the constellation Sagittarius) because it is obscured by the close-packed stars and cosmic dust that comprise the Milky Way.

But radio waves pass through cosmic dust clouds. By tracking the 21-cm. waves given off by hydrogen, radio astronomers have been able to probe deeper and deeper through the Milky Way toward the galaxy’s center. Recently, Dutch Astronomers G. W. Rougoor and J. H. Oort of Leiden Observatory reported that they had been able to peer into the mysterious nucleus itself. They found there a strange pinwheel of rapidly spinning hydrogen.

Matter of Time. The sun is far out on one of the spiral arms of the galaxy, about 25,000 light-years from its center. Technically, the astronomers can only see what no longer exists, or rather what existed 25,000 years ago, when the radio waves they observe left the galaxy’s center. But in cosmological time, 25,000 years is only the blink of an eye, and astronomers, faced with the huge intervals of space, use light-years as simple measures of distance.

The Dutch astronomers found that for 15,000 light-years toward the center, clouds of hydrogen fill the spaces between the stars, revolve around the center with reasonably circular motion. Then, 10,000 light-years out from center, comes a rather dense spiral arm of hydrogen that is moving away from the center at 100,000 m.p.h. Other hydrogen clouds in the vicinity may be moving outward as fast as 400,000 m.p.h.

Fiery Pinwheel. Behind these out-streaming clouds Rougoor and Oort found a ring of hydrogen about 300 light-years wide and encircling the galaxy’s center at a distance of 1,600 lightyears. It appears to be revolving at a good clip (600,000 m.p.h.). Inside it is a band of almost empty space; then comes a rotating disk of hydrogen whose density increases toward the center. Neither ring nor disk appears to be moving outward. They are like the solid part of a fireworks pinwheel, which spins rapidly and throws off spirals of sparks.

Rougoor and Oort are not sure how to interpret their observations. They suspect that the hydrogen disk at the center of the galaxy is rich in stars, but they cannot see them. The stars and hydrogen, they say, are presumably held together by gravitation and revolve more or less as a unit. The outstreaming hydrogen beyond the ring is hard to explain. They calculate that at the present rate of flow, all the hydrogen should have been drained from the nucleus in a mere 10 million to 100 million years, which is only a tiny part of the life span of a galaxy. Since the nucleus is not drained, its hydrogen must be replenished somehow. Rougoor and Oort suggest that the replenishing hydrogen may come from the corona of thinly scattered hydrogen atoms that surrounds the whole galaxy like a huge spherical cocoon 80,000 light-years wide, working its way into the spinning disk at the top and bottom.

* Only heavenly body visible to the naked eye that is not part of earth’s own galaxy is M 31 (in the constellation of Andromeda), a galaxy 2,000,000 light-years away. Through high-powered telescopes, astronomers have detected millions of other galaxies, presume there are billions more beyond man’s ken.