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B seems to be the answer as....
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.

If the cluster of stars are there at the center then it will preclude/reject the other astronomical phenomena that have been observed at the center of M87 galaxy.

Between E and B

I think we all agree that the question is asking which answer undermines the fact that the core of M87 is a cluster of stars. We need an answer that supports the explanation that the core is a black hole.

The answer to the question is provided by the last sentence:

" If the center of NGC 4258 were a star cluster, the stars would be so closely spaced that collisions between individual stars would have long ago torn the cluster apart."

Answer B states that a cluster of stars at the center will preclude (or, eliminate the possibility of) the existance of other astronomical phemonema (black holes). This answer supports (not undermines) the explanation.

Answer C states that the stars in M87 are not as closely spaced as in other galaxies. If the center is made entirely of closely packed stars, this will not give M87 the needed core density to observe the whirling gas clouds. The explanation that supports this would be a black hole.

The answer is C.

I think E because the passage says "most astronomers believe that the large concentration of mass at galaxy center is causing the gas to whirl"

I just read your explanations. Oh so we're trying to prove that M87 is a black hole and so B says that phenomena that was observed at center M87 could only occur with cluster of stars at the center. I think I get it.

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GMATJunky

Even I think the answer is E. I feel B is denying the observation which is incorrect. Dana J what are your thoughts on this one?

IMO E

I go for B as the premise of the question ask for reason to UNDERMINE the explanation that at the center of M87, there won't have any Blackhole AND in answer B: preclude the existence of CONTEMPORARY phenomena observed in M87 -> it can't be a cluster of stars.

I go between B and E.
A last paragraph mentions that the black hole does not exist if
C This is the fact does not undermine the whirling gas.
D Example of Other galaxy, it does not undermine the whirling gas

Have hard time to distinguish the correct answe between B and E

The questions asks which could undermine the possibility of billion dim stars. We have to show that the core density(which needs to be calculated from the velocity) needs to be high to negate the condition.

A The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.

This is not correct as it affirms the possibility of the star cluster.


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.

Possible answer.


C The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87.


This explains that the core density is not as high as NGC 4258. So not correct.

D Only one other galaxy has been observed to contain gas clouds whirling about its center as they do about the core of M87.

This is not clear, which galaxy is it talking about hence discard.


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 restates the fact already explained in the paragraph.

My answer is (B). Can anyone please explain if I am correct ?

B

IMO (B)
(E) & (A) are similar in meaning.

OA ?

The question is more like a CR question where it is asked to undermine the situation.
Now it is clearly asking for another evidence that can show that the whirling of gas can be possible for reasons other that the black hole.
E is the correct answer

The passage says- according to some skeptics the reason for the whirling of gas is likely to be a cluster of stars. So the assumption is that the cluster of stars causes the whirling of gas. To weaken this hypothesis, we've to find a reason that negates/undermines the skeptics' hypothesis.

Choice B states that a cluster would preclude certain other observed phenomena. One of the observed phenomena is 'whirling gas'. And if the cluster precludes it, then there'd be no observed phenomenon of whirling gas. Since whirling gas is present on M87, there won't be any clusters of stars. Therefore the skeptics' hypothesis that the cluster is causing the whirling of gas is false. Hence B is the credited answer.

Choices A & E strongly support skeptic's explanation and choices C&D are out of context, so eliminate A, E, C, & D.

this queston took very long time but still not sure about the answer

Let it B.