No. 56: Mar-Apr 1988
Can we believe our eyes? Dare anyone suggest that black holes do not lurk out in the cosmos sucking in stars and unwary spaceships? It's all true; an arti cle bearing the above title appeared in the January 1988 number of Sky and Telescope. Doubts do surface once in a while, despite all the TV documentaries, all the textbooks, and all the newspaper jottings, where black holes are described in the hushed tones used only with profound truths of nature.
To set the stage, we quote a paragraph from said article:
"There is, however, a serious problem with black holes, one that leaves some scientists skeptical about their existence. The overarching mystery lies hidden at a hole's center. Einstein's general theory of relativity predicts that we will find there an object more massive than a million Earths and yet smaller than an atom -- so small, in fact, that its density approches infinity. The idea of any physical quantity becoming infinite flies in the face of everything we know about how nature behaves. So there is good reason to be skeptical that such a nasty thing could happen anywhere at all."
Among the observations that hint at the reality of black holes are the X-ray binaries. In a typical X-ray binary, prodigious, flickering fluxes of X-rays reveal the presence of an ultradense star and an orbiting companion. The rapid orbital motion of the companion star tells us that the central X-ray star has a mass of more than three suns. General Relativity assures us that such a star can only collapse further to form a black hole. Therefore, black holes must exist.
J. McClintock, the author of this article, does not buy this reasoning. General Relativity, he says, has been shown to be valid so far only in weak gravitational fields, not in the very powerful gravitational fields of an X-ray star. "...we presume that Einstein's theory correctly describes strong gravity when we argue that certain X-ray stars are black holes, yet, at the same time, these alleged black holes are the acid test of Einstein's theory of strong gravity." (McClintock, Jeffrey; "Do Black Holes Exist?" Sky and Telescope, 75:30, 1988.)
Comment. The long history of science teaches us that all theories are eventually displaced by more accurate, more all-inclusive formulations. Unfortunately, this makes textbook writing difficult.
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