Lunar sight-seeing trips and orbiting space hotels are within reach, moon wal

游客2023-12-21 40

问题 Lunar sight-seeing trips and orbiting space hotels are within reach, moon walking astronaut Edwin"Buzz" Aldrin said last week, but some who favor space tourism worried about its "giggle factor". Astronomers have known for years that a source of intense energy emissions lies at the center of the Milky Way Galaxy, obscured from view by vast clouds of dust and gas. In February, 1992, researchers at the Max Planck Institute in Garching, Germany, reported evidence that the mysterious energy source is a gigantic black hole.
Observations have shown that many strong energy sources lie at the heart of the Milky Way. One of them, called Sagittarius A, is thought to be the actual center of the Galaxy, the point about which the great spiral of stars rotates. Sagittarius A is a powerful emitter of radio waves and X-rays.
Astronomers have considered two possible explanations for the identity of Sagittarius A. They theorized that it is either a compact duster of normal stars or a super-massive black hole containing as much as a million or more suns. The German scientists reported that they found strong evidence in support of the black hole explanation.
The astronomers used a new telescope high in the Andes Mountains of Chile to obtain the sharpest images ever made of the region around Sagittarius A. The image shows that Sagittarius A is a single, small object rather than a duster of stars.
The researchers also found that a bubble of gas is expanding outward from Sagittarius A. This expanding gas is similar in temperate, density, and composition to the jets of gas that astronomers have observed flow hag away from the centers of many other galaxies. Such jets are thought to be generated by accretion disks surrounding enormous black holes. Accretion disks are vast, swirling masses of gas and dust that give off titanic amounts of energy as they are sucked into the black hole. The similarity between the jets emitted by some galaxies and the gas bubble surrounding Sagittarius A supports the idea that Sagittarius A is a super-massive black hole. [br] Sagittarius A is ______.

选项 A、clearly a super-massive black hole
B、a compact cluster of normal stars
C、a single, small subject
D、still an issue of controversy

答案 D

解析文章第三段指出，天文学家对于Sagittarius A的身份提出了两种可能的解释，而综观全文可知，尽管他们发现了一些用来证明Sagittarius A是黑洞的证据，但这毕竟在整个科学界尚未形成定论，因此[D]为正确答案。

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