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.
According to the passage, the dynamical evidence referred to in lines 9–10(shown in boldface) supports which of the following?
A:Recent assumptions about the velocities of stars
B:Widely held predictions about the amount of matter a black hole will engulf
C:The existence of an extremely dense object at the center of the Milky Way
D:The contention that too much energy is coming from the mass at the Milky Way's galactic center for that mass to be a black hole
E:The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole
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：
C:The existence of an extremely dense object at the center of the Milky Way
答案 C
文章中提到的动力学证据支持什么?文章指出，动力学证据表明在银河系中心有一个质量是太阳质量200万到300万倍的极其致密的物体。一个具有如此质量的极其致密的物体，其密度当然是非常大的。
A.这篇文章不是在暗示上面提到的动力学证据支持关于恒星速度的假设。相反，它指出关于恒星速度的假设已经“最近得到证实”，而动力学证据实际上是基于这些假设。如果动态证据是这些假设的产物，那么它就不能用来支持这些假设。
B.这篇文章表明，动力学证据与银河系中存在的一个密度极高的物体是一致的，它很可能是一个黑洞。然而，这些证据绝不意味着可以对这样一个假设的黑洞会吞噬多少物质做出可靠的预测。
C.正确。如上所述，这指的是具有巨大质量的极其致密的物体;这个物体当然会“密度极高”。D. 这个选项提出的建议与文中信息相反。这段文字表明，银河系中心的这个物体实际上辐射得太少，很难被确认为黑洞。
E.这篇文章承认银河系中心质量的密度与黑洞的存在是一致的。然而，这篇文章进一步表明，从银河系中心向外辐射出的能量数量少得出人意料，这让人产生了疑问。
文章中提到的动力学证据支持什么?文章指出，动力学证据表明在银河系中心有一个质量是太阳质量200万到300万倍的极其致密的物体。一个具有如此质量的极其致密的物体，其密度当然是非常大的。
A.这篇文章不是在暗示上面提到的动力学证据支持关于恒星速度的假设。相反，它指出关于恒星速度的假设已经“最近得到证实”，而动力学证据实际上是基于这些假设。如果动态证据是这些假设的产物，那么它就不能用来支持这些假设。
B.这篇文章表明，动力学证据与银河系中存在的一个密度极高的物体是一致的，它很可能是一个黑洞。然而，这些证据绝不意味着可以对这样一个假设的黑洞会吞噬多少物质做出可靠的预测。
C.正确。如上所述，这指的是具有巨大质量的极其致密的物体;这个物体当然会“密度极高”。D. 这个选项提出的建议与文中信息相反。这段文字表明，银河系中心的这个物体实际上辐射得太少，很难被确认为黑洞。
E.这篇文章承认银河系中心质量的密度与黑洞的存在是一致的。然而，这篇文章进一步表明，从银河系中心向外辐射出的能量数量少得出人意料，这让人产生了疑问。
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