Twinkle, Twinkle 3C-273

Seen through the finest optical telescopes, the five nondescript points in the sky looked like ordinary stars. To radio astronomers though, they sounded uncommonly noisy. For some strange reason they were all exceptionally powerful radio transmitters--electronic extroverts among the quiet billions of other stars that keep almost perfect radio silence.

Astronomers were stumped by the bright, mysterious bodies. What was causing all the radio noise? Even photographs of the stars' spectra--all the wave lengths of emitted light, from red to violet--were no help. A star's spectrum is its individual signature, but none of these five spectra bore any resemblance to the spectrum of any other star.

Big Shift. Then Drs. Jesse L. Greenstein of Caltech and Maarten Schmidt of Mount Wilson and Palomar observatories decided to test a novel theory. When any object is moving away from the earth at a speed that is close to the speed of light, its light waves appear to slow down in frequency. Bright bands of the spectrum that are normally blue show up as yellow. Yellow bands become red. Stars have never been known to move fast enough to show such large light shifts, so Drs. Greenstein and Schmidt studied the strange spectra just as if they came from another type of swiftly receding object.

The trick worked. The spectrum of one of the radio stars, 3C-273, turned out to be the spectrum of an object racing away from the earth at 31,000 miles per sec., one-sixth the speed of light. But only galaxies, which get their speed from the general expansion of the universe, can move that fast. The astronomers concluded that they were dealing not with a star but with an entire distant galaxy.

Now there were more problems. According to the rules that govern the expanding universe, a galaxy moving at one-sixth the speed of light must be 2 billion light-years away. But how could 3C-273 be so far away and still so bright?

Greenstein and Schmidt turned to another one of the five bright radio stars. The spectrum of 3C-48, they discovered, is even more peculiar than 3C-273. Study showed that its brightly visible light has shifted so far it must come from a galaxy receding from the earth at one-third the speed of light. It must be 3.6 billion light-years away. To look like a bright star despite its enormous distance, 3C-48 must give off 100 times as much light as the entire Milky Way galaxy with its 100 billion stars.

Caught in the Act. Why this startling brilliance? In the vigorous radio waves emitted by both galaxies, the astronomers found a probable explanation. Other powerful radio sources are galaxies that have apparently exploded, spewing into space vast clouds of nonluminous turbulent gas that still generate radio waves after millions of years (TIME, Feb. 8). These galaxies, too, were probably abnormally brilliant in visible light soon after they exploded. Astronomers now feel sure that 3C-273 and 3C-48, the brightest things in the universe, are galaxies caught in the very act of explosion.

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