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  3. Black holes are one of only a fairly small number of cases in the history of science in which a theory was developed in great de

Black holes are one of only a fairly small number of cases in the history of science in which a theory was developed in great de

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问题    Black holes are one of only a fairly small number of cases in the history of science in which a theory was developed in great detail as a mathematical model before there was any evidence from observations that it was correct. 【F1】Indeed, this used to be the main argument of opponents of black holes: how could one believe in objects for which the only evidence was calculations based on the dubious theory of general relativity? In 1963, however, Maarten Schmidt, an astronomer at the Palomar Observatory in California, measured the red shift of a faint starlike object in the direction of the source of radio waves called 3C273. He found it too large to be caused by a gravitational field: if it had been a gravitational red shift, the object would have to be so massive and so near to us that it would disturb the orbits of planets in the Solar System. 【F2】This suggested that the red shift was instead caused by the expansion of the universe, which, in turn, meant that the object was a very long distance away. And to be visible at such a great distance, the object must be very bright, must, in other words, be emitting a huge amount of energy. 【F3】The only mechanism that people could think of that would produce such large quantities of energy seemed to be the gravitational collapse not just of a star but of a whole central region of a galaxy.
   Further encouragement for the existence of black holes came in 1967 with the discovery by a research student at Cambridge, Jocelyn Bell-Burnell, of objects in the sky that were emitting regular pulses of radio waves. At the seminar at which Bell and her supervisor announced their discovery, I remember that they called the first four sources to be found LGM 1-4, LGM standing for "Little Green Men." In the end, however, they and everyone else came to the less romantic conclusion that these objects were in fact rotating neutron stars (中子星) that were emitting pulses of radio waves because of a complicated interaction between their magnetic fields and surrounding matter. 【F4】This was bad news for writers of space westerns, but very hopeful for the small number of us who believed in black holes at that time: it was the first positive evidence that neutron stars existed. A neutron star has a radius of about ten miles, only a few times the critical radius at which a star becomes a black hole. 【F5】If a star could collapse to such a small size, it is not unreasonable to expect that other stars could collapse to even smaller size and become black holes.
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答案事实上这曾是黑洞反对者的主要论据：黑洞存在唯一的依据是基于不太可靠的广义相对论的计算结果，这如何能让人相信黑洞的存在?
解析 ①本句是由冒号连接的两个分句，分句1是主系表结构，分句2是反问句。分句2是对分句1中的the main argument作进一步解释说明。②分句2中带有for which引导的定语从句修饰objects，说明这个证明黑洞存在的唯一依据不能让人信服。句末的based on the dubious theory of general relativity是过去分词短语作后置定语，修饰calculations，说明该计算结果是“基于不太可靠的广义相对论”得出的。
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