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Astronomers theorize that a black hole forms when a massive object shrinks catastrophically under its own 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 gal- axy’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 mea- sured the speed of a ring of dust and gas rotating close to the galaxy’s (30)center. From its speed, they calcu- lated 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.
Which of the following, if true, would most clearly undermine the possible explanation for the whirling gas in M87 that is mentioned in the last sentence of the first paragraph?
A The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
B A cluster of stars at the center would preclude the existence of certain other astronomical phenomena that have been observed at the center of M87.
C The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87.
D Only one other galaxy has been observed to contain gas clouds whirling about its center as they do about the core of M87.
E The gravitational force of a cluster of a billion or so dim stars would be sufficient to cause a whirling ring of gas and dust to collect around the center of a galaxy.
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Re: Astronomers theorize that a black hole forms when a
[#permalink]
Updated on: 15 May 2008, 09:21
A few skeptics have argued that the concentration of mass necessary to explain the speed of the whirling gas is not necessarily a black hole: the concentration in M87 might be a cluster of a billion or so dim stars.
We are asked to undermine the explanation that in M87 wind may be due to a cluster of a billion or so dim stars, Now hows that B undermine that?
B. A cluster of stars at the center would preclude the existence of certain other astronomical phenomena that have been observed at the center of M87.
***EDITED**** BTW, OA is given as A which obviously does not make sense.
Originally posted by mbawaters on 15 May 2008, 09:01.
Last edited by mbawaters on 15 May 2008, 09:21, edited 1 time in total.
Re: Astronomers theorize that a black hole forms when a
[#permalink]
15 May 2008, 09:16
1
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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.
To undermine this explanation - we either need an alternative expl that causes the gases to whirl or somehow prove that there is no blackhole at the center of the galaxy.
Which of the following, if true, would most clearly undermine the possible explanation for the whirling gas in M87 that is mentioned in the last sentence of the first paragraph?
A The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart. >> doesnt tell us if that gravitational force can cause these gases to whirl.
B A cluster of stars at the center would preclude the existence of certain other astronomical phenomena that have been observed at the center of M87. >> that other astronomical phenomena may not be referring to "black holes" - this choice is too broad.
C The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87. >> Irrelevant.
D Only one other galaxy has been observed to contain gas clouds whirling about its center as they do about the core of M87. >> Irrelevant.
E The gravitational force of a cluster of a billion or so dim stars would be sufficient to cause a whirling ring of gas and dust to collect around the center of a galaxy. >> This is suggesting that we dont need a black hole to create the type of gravitational force. [/quote]
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Re: Astronomers theorize that a black hole forms when a
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25 Jul 2020, 16:42
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