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# Astronomers theorize that a black hole forms when a massive

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VP
Joined: 03 Apr 2007
Posts: 1367
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Kudos [?]: 637 [0], given: 10

Astronomers theorize that a black hole forms when a massive [#permalink]

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09 Jul 2008, 23:34
Astronomers theorize that a black
hole forms when a massive object
shrinks catastrophically under its own
Line gravity, leaving only a gravitational
(5)field so strong that nothing escapes it.
Astronomers must infer the existence
of black holes, which are invisible,
from their gravitational influence on
the visible bodies surrounding them.
(10)For example, observations indicate
that gas clouds in galaxy M87 are
whirling unusually fast about the galaxy’s
center. Most astronomers
believe that the large concentration
(15)of mass at the galaxy’s center is a
black hole whose gravity is causing
the gas to whirl. A few skeptics have
argued that the concentration of mass
necessary to explain the speed of the
(20)whirling gas is not necessarily a black
hole: the concentration in M87 might
be a cluster of a billion or so dim stars.
The same hypothesis might have
been applied to the galaxy NGC 4258,
(25)but the notion of such a cluster’s
existing in NGC 4258 was severely
undermined when astronomers measured
the speed of a ring of dust and
gas rotating close to the galaxy’s
(30)center. From its speed, they calculated
that the core’s density is more
than 40 times the density estimated
for any other galaxy. If the center of
NGC 4258 were a star cluster, the
(35)stars would be so closely spaced
that collisions between individual
stars would have long ago torn the
cluster apart.
--------------------------------------------------------------------------------
Q10:
The skeptics mentioned in the first paragraph would be most likely to agree with the
astronomers mentioned in line 13 about which of the following statements concerning
the galaxy M87?
A. The speed of the gas whirling around the center of M87 is caused by a dense
object that is not a black hole.
B. The concentration of mass at the center of M87 is probably a large cluster of
dim stars.
C. The presence of a black hole at the center of M87 is the most likely
explanation for the speed of the gas whirling about the galaxy’s core.
D. The speed of the gas whirling around the center of M87 is caused by a large
concentration of mass at the core of M87.
E. The gravitational influence of a star cluster would not be strong enough to
account for the speed of the gas whirling around the core of M87.
If you have any questions
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SVP
Joined: 28 Dec 2005
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10 Jul 2008, 05:45
i would pick D for this one. We have to avoid answer choices that specify one choice and focus on an answer choice that both parties would agree with ...
Senior Manager
Joined: 10 Mar 2008
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10 Jul 2008, 12:21
D for me as well to keep both parties satisfied
Manager
Joined: 04 Jun 2008
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10 Jul 2008, 12:28
C. The presence of a black hole at the center of M87 is the most likely
explanation for the speed of the gas whirling about the galaxy’s core.

D. The speed of the gas whirling around the center of M87 is caused by a large
concentration of mass at the core of M87.

between C and D ..
first paragraph says about massive concentration does not talk about black hole ..so C is out.

vote for D
VP
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Posts: 1367
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Kudos [?]: 637 [0], given: 10

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10 Jul 2008, 12:32
OA is D
Re: RC-Astronomers   [#permalink] 10 Jul 2008, 12:32
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# Astronomers theorize that a black hole forms when a massive

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