Two Million Suns

Astronomer Nicholas U. Mayall of Lick Observatory, Calif., was taking routine pictures of N.G.C. 6964, a spiral nebula four million light-years away. On one of the plates last week his practiced eye discovered a monstrous star that should not have been there. It was a supernova, an obscure star that had exploded suddenly. When Dr. Mayall photographed it first, its "absolute brilliance" was equal to two million suns. It had probably faded from a peak a few weeks ago of four million suns. If any planets had been revolving around that unstable star, they were certainly vaporized by now into scattered atoms.

Explosions of supernovae are the most spectacular phenomena in the universe, and among the most mysterious. Fortunately for everybody except impatient astronomers, they do not seem to occur very often. Each star system, such as N.G.C. 6964 and the earth's own Milky Way galaxy, is thought to average one such catastrophe in about 600 years. The brightest local outburst, thought to be a supernova, was Tycho's Star, which exploded in 1572 and was bright enough to be seen in daytime.

No one knows for certain what makes supernovae explode. One theory: when they reach some unstable state their matter "collapses." The electrons circling around the atomic nuclei move inward and combine with the equal number of protons that they find in the nucleus, forming neutrons. These occupy very little space compared with the original atom, and can pass through ordinary matter.

Attracted by gravitation, they flash down to the center of the star, releasing enormous energy. The reaction may spread in a short time through most of the mass of the star. The energy released is enough to blow off the star's outer layer. All that remains, according to this theory, is a small, dense core of neutrons and a vast shell of flaming gas that burns itself out in a few months of splendor.

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