X Rays from a Quasar

Quasars, most astronomers agree, are the oldest, brightest, farthest and most mysterious celestial objects known to man. To this list of superlatives, scientists at the Naval Research Laboratory have now added another. After recording X rays emanating from quasar 3C 273--the first time that a quasar has been identified as an X-ray source --Physicists Herbert Friedman and Edward Byram have determined that 3C 273 is also the most powerful X-ray emitter ever discovered.

The latest addition to quasar knowledge was obtained by instruments carried aboard an Aerobee rocket shot from White Sands, N. Mex., in May. Soaring above the atmosphere, which absorbs X rays before they reach the earth, the rocket detected X-radiation from quasar 3C 273, from a giant elliptical galaxy called M 87, and from three locations in the sky where no celestial objects are visible. The recorded radiation from the quasar was only one-thousandth as great as that from a starlike object called Sco XR-1--which appears to be the brightest X-ray emitter in the sky (TIME, Sept. 16). But 3C 273 is 1.5 billion light-years away, compared with only 500 light-years for Sco XR-1. The quasar's actual X-radiation is thus about one billion times that of Sco XR-1, the scientists calculate, and 500 times as powerful as that of M 87, a galaxy consisting of a trillion stars.

Astronomer Friedman would like next to monitor 3C 273's X-ray luminosity to determine if it varies as widely as the quasar's visible light. He would also like to get an X-ray spectrum, which might help unlock more of the quasars secrets. Either procedure would require a longer look at quasar X rays than can be obtained during the fleeting minutes that an X-ray telescope can be rocketed above the earth's atmosphere. The answer, Friedman says, is an X-ray telescope in an orbiting satellite or, better yet, one on the surface of the moon.

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