题目信息
This passage is excerpted from material published
in 1997.
Is there a massive black hole at the center of our
galaxy, the Milky Way? The evidence is inconclusive.
Just as the Sun's mass can be determined, given
knowledge of other variables, by the velocity at
which its planets orbit, the mass at the center of the
Milky Way can be revealed by the velocities of stars
and gas orbiting the galactic center. This dynamical
evidence, based on recently confirmed assumptions
about the stars' velocities, argues for an extremely
compact object with a mass two to three million
times the mass of our Sun. Although according to
current theory this makes the mass at the center
of the galaxy too dense to be anything but a black
hole, the relative lack of energy radiating from the
galactic center presents a serious problem. A black
hole's gravity attracts surrounding matter, which
swirls around the black hole, emitting some energy
as it is engulfed. Scientists believe that the amount of
energy that escapes the black hole should be about
10 percent of the matter's rest energy (the energy
equivalent of its mass according to the equation
E=mc2). But when the energy coming from the
galactic center is compared towidely held predictions
based on how much matter should be falling into a
theoretical central black hole, there is a discrepancy
by a factor of a few thousand.
in 1997.
Is there a massive black hole at the center of our
galaxy, the Milky Way? The evidence is inconclusive.
Just as the Sun's mass can be determined, given
knowledge of other variables, by the velocity at
which its planets orbit, the mass at the center of the
Milky Way can be revealed by the velocities of stars
and gas orbiting the galactic center. This dynamical
evidence, based on recently confirmed assumptions
about the stars' velocities, argues for an extremely
compact object with a mass two to three million
times the mass of our Sun. Although according to
current theory this makes the mass at the center
of the galaxy too dense to be anything but a black
hole, the relative lack of energy radiating from the
galactic center presents a serious problem. A black
hole's gravity attracts surrounding matter, which
swirls around the black hole, emitting some energy
as it is engulfed. Scientists believe that the amount of
energy that escapes the black hole should be about
10 percent of the matter's rest energy (the energy
equivalent of its mass according to the equation
E=mc2). But when the energy coming from the
galactic center is compared to
based on how much matter should be falling into a
theoretical central black hole, there is a discrepancy
by a factor of a few thousand.
The "serious problem" referred to in line 17 (underlined) could be solved if which of the following were true?
A:Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
B:Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low.
C:The object at the center of the Milky Way turned out to be far more dense than it is currently estimated to be.
D:The object at the center of the Milky Way turned out to be far more massive than it is currently estimated to be.
E:Matter being engulfed by a black hole radiated far more energy than is currently assumed.
参考答案及共享解析
共享解析来源为网络权威资源、GMAT高分考生等； 如有疑问，欢迎在评论区提问与讨论
本题耗时：
已选答案：
正确答案：
A:Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
答案 A
如果这五种选择中的一种是正确的，那么这五种选择中哪一种将表明有可能解决所提到的严重问题?这个严重的问题据说是由于从银河系中心辐射出的能量相对不足，如果一个吞噬物质的黑洞真的在银河系中心的话，辐射能量就会相对不足。根据这篇文章，从理论上讲，从被假设的黑洞吞没的物质中辐射出来的能量比预期要少几千倍。然而，如果发现被吞没的物质比先前估计的少几千倍，那么观测到的相对较低水平的辐射能量就不再与假设的黑洞的存在相矛盾了。
A.正确。重新审视这些被广泛接受的预测背后的假设，可能会导致修正后的预测与有关星系中心辐射能量的观测证据相一致。
B.这篇文章说，假定的被吞没物质的数量已经显得太少了;这个答案的选择实际上会使文章中的“严重问题”变得更糟。也就是说，假设有更多的物质被如此少量的辐射吞噬，只会使问题更加严重。
C.这篇文章并没有具体说明高于估计的密度对辐射的能量有什么影响。也就是说，即使更大的质量会改变预测，更大的密度可能也不会。
D.如果物体质量更大，那么被这个假设的更大的黑洞吞噬的物质可能会辐射出比观测到的更大的能量。这只会让“严重问题”更加严重。
E.由于目前观测到的辐射能不足，如果发现被吞没的物质辐射出的能量比预期的还要多，就会使“严重问题”严重得多。也就是说，观测到的相对较低的辐射能量将比预期的量少得多。
如果这五种选择中的一种是正确的，那么这五种选择中哪一种将表明有可能解决所提到的严重问题?这个严重的问题据说是由于从银河系中心辐射出的能量相对不足，如果一个吞噬物质的黑洞真的在银河系中心的话，辐射能量就会相对不足。根据这篇文章，从理论上讲，从被假设的黑洞吞没的物质中辐射出来的能量比预期要少几千倍。然而，如果发现被吞没的物质比先前估计的少几千倍，那么观测到的相对较低水平的辐射能量就不再与假设的黑洞的存在相矛盾了。
A.正确。重新审视这些被广泛接受的预测背后的假设，可能会导致修正后的预测与有关星系中心辐射能量的观测证据相一致。
B.这篇文章说，假定的被吞没物质的数量已经显得太少了;这个答案的选择实际上会使文章中的“严重问题”变得更糟。也就是说，假设有更多的物质被如此少量的辐射吞噬，只会使问题更加严重。
C.这篇文章并没有具体说明高于估计的密度对辐射的能量有什么影响。也就是说，即使更大的质量会改变预测，更大的密度可能也不会。
D.如果物体质量更大，那么被这个假设的更大的黑洞吞噬的物质可能会辐射出比观测到的更大的能量。这只会让“严重问题”更加严重。
E.由于目前观测到的辐射能不足，如果发现被吞没的物质辐射出的能量比预期的还要多，就会使“严重问题”严重得多。也就是说，观测到的相对较低的辐射能量将比预期的量少得多。
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