Littlest Star

Astronomer Willem J. Luyten of the University of Minnesota is the world's leading small-star fancier. Last week he was beaming over the smallest star yet discovered: a "white dwarf," 25 light years away from the earth, which he found and analyzed with the help of Dr. E. F. Carpenter of the University of Arizona. The littlest star (Catalog No. L 886-6) is hot (15,000DEG to 20,000DEG F.), and it shines with a white light. But it is only 2,500 miles in diameter, not much larger than the moon.

In mass, however, the star is no midget. Astronomer Luyten figures that it is 40% heavier than the sun. A cubic inch of its densely packed matter would weigh something like 1,000-tons, and if a 150-lb. man could stand on its surface, his body would weigh 300,000 tons.

Sky Pensioners. Such strange, dim little stars have long fascinated astronomers. Some believe that dwarfs are the source of the radio waves that beat on the earth from points in space that are apparently empty. One theory holds that they are senile stars which have expended most of their energy, turning into "degenerate matter." They are now living economically, like old people on pensions, but at last their feeble light will die. Then they will turn into "black dwarfs," cruising invisibly through space.

Theories disagree about this dense, degenerate matter. Some think that it is a brew of atoms that have been stripped of circling electrons. Since nearly all the bulk of a normal atom (as known on earth) is empty space inside the orbits of its electrons, the stripping-down process would allow nuclei and electrons to be packed much more tightly.

Astronomer Fritz Zwicky of Cal Tech thinks there is another way to pack matter tightly. Normal atoms contain one electron for each proton in the nucleus. If the electrons could be persuaded to unite with the protons, each pair would form a neutron. This reaction does not take place under normal conditions; the electrons circle forever, and the protons stay in the nucleus. But Zwicky believes that under the strange and violent conditions that exist in certain large stars, electrons may unite with protons.

The neutrons formed in this way can pass through ordinary matter. They would trickle down quickly to the center of the star. Falling for great distances under strong gravitational forces, they would release enormous amounts of energy. If enough of them fell at the same time, they would blow the whole star to bits. It would glory briefly as a supernova, shining more brightly than all the stars in the sky. But when the excitement was over, the only thing left would be a "neutron-star": a ball of peculiar matter made largely or entirely of neutrons. A cubic inch of this strange stuff would weigh 18 million tons, and a mass the size of the sun could be packed into a sphere less than 100 miles in diameter.

Blended Light. While a neutron-star might be luminous, it would probably be too small to be seen in any telescope. But Zwicky believes that it will act as a "gravitational lens." The gravitational field around it will be so intense that it will bend all light coming near it. Some rays, passing close, will be turned back on their tracks. Others will be turned less sharply. The result in the telescope's eye will be a faint disk of light made up of small contributions from all the stars in the universe. This blended light should be possible to identify with a spectroscope.

After watching the sky for ten years now, Zwicky has found no such star, but he has not given up. The 48-in. Schmidt telescope on Palomar Mountain may soon be fitted with powerful spectroscopic equipment. With this Zwicky hopes he will find a tiny neutron star made visible by the light-bending power of its gravitational lens.

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