Science: Giant to Dwarf

The sun is quite an ordinary star, some what smaller than the average visible stars.

It has a diameter of 864,000 miles, a surface temperature of 6,000° C. which increases to an estimated 20,000,000° at the core. It looks like a simple ball of hot matter but actually it is a complicated engine of energy production. It shines so steadily that to laymen it seems changeless.

Actually it was another sort of star in the distant past and it will be still another sort of star in the distant future.

Latest and most informing biography of the star that sustains all life of earth was published this week by Professor George Gamow ( The Birth and Death of the Sun — Viking — $3). A distinguished Russian-born physicist who is now at George Washington University (Washington, D. C.), author of a recent popularization of physics called Mr. Tompkins in Wonderland, Dr. Gamow writes clearly and imaginatively, knows when to stop short of over taxing lay readers. Some of his premises in The Birth and Death of the Sun are speculative and controversial, but they are based on the best recent investigations and they are never implausible.

In the beginning Dr. Gamow pictures an enormously hot, tremendously dense gas expanding in space. As it expanded, it thinned and cooled. Chance aggregations began to clump together out of the mass, to contract by gravity. These were infant stars. They were very large, and diffuse, relatively cool.

The sun passed its first youth as a red giant star, like the one in the constellation Auriga which has about 4,000,000 times the sun’s volume but only 15 times its mass, and which is only .000005 as dense as water. But as red giants contract, they get hotter, as air in a pump gets hotter when it is compressed. The sun appears to be some two billion years old now, and it is hot enough to live on atomic energy, converting hydrogen into radiation.

It used to be thought that as the sun used up its fuel, it would grow colder & colder, that the end of life on earth would be a freeze-out. Dr. Gamow’s own researches show that as the sun converts more & more hydrogen into energy, it must get continually hotter. Toward the end of its hydrogen supply, Gamow estimates, the sun’s radiation will have increased a hundredfold. Thus a heat-death instead of a cold-death is threatened for earthlings.

“The oceans and seas,” says Dr. Gamow, “will boil. It is difficult to imagine any living being left on the surface of the earth under such conditions, though the progress of technique during the next few billions of years . . . may make it possible to dig safe, air-conditioned underground cellars for humanity or even to transport the whole population of the earth to some distant planet. . . .” Even at the increasing rate of hydrogen consumption, the sun has enough left for ten billion years. Thus it has five-sixths of its life to live as a normal star. But when the hydrogen is gone at last, it will grow cooler, collapse into an enormously dense, feebly shining dwarf star, with its fragments of ruined atoms crushed tightly together. Such dense dwarf stars are already known to astronomers; one of them is the dim companion of bright Sirius.

The temperature on earth will fall 200° below zero C. Finally the dying sun will completely die—it will be as cold as surrounding space, emit no light at all.

In such a state the sun will be not much larger than the earth is now, and a pint of its substance will weigh 3,000,000 Ib.

There is a chance that, before it reaches this end of the trail, the sun will flare up as a “nova” or new star, increasing in brightness some 200,000 times. So many novae have been spotted in the sky that astronomers believe every normal star may have an outburst at least once in its lifetime. The star may return to its ordinary state and continue its evolution, but if the sun flared up it would vaporize every planet in the solar system. This might happen at any time. However, since the sun has ten billion years to go, the chances of a nova outburst in any century are only 1 in 100,000,000.