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19 Jan 2023, 22:26
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3. 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?
What is the possible explanation for the whirling gas in M87 that is mentioned in the last sentence of the first paragraph?
It is: the concentration in M87 might be a cluster of a billion or so dim stars.
We need to undermine this explanation. So we need to give why the mass concentration may not be a cluster of stars.
(A) The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
This doesn't undermine that it could be a cluster stars. It is saying that the stars could exist as a cluster without being torn 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.
Correct. This says that if it were a cluster of stars, then certain other astronomical phenomena that have been observed was not possible. Hence, this suggests that it is not a cluster of stars.
(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 tells us that it could be cluster of stars because they can exist close together (because they do exist even closer together in another galaxy) without being torn apart.
(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 says that it could be a cluster of stars because their gravitational pull would be sufficient.
Answer (B)
What is the possible explanation for the whirling gas in M87 that is mentioned in the last sentence of the first paragraph?
It is: the concentration in M87 might be a cluster of a billion or so dim stars.
We need to undermine this explanation. So we need to give why the mass concentration may not be a cluster of stars.
(A) The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
This doesn't undermine that it could be a cluster stars. It is saying that the stars could exist as a cluster without being torn 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.
Correct. This says that if it were a cluster of stars, then certain other astronomical phenomena that have been observed was not possible. Hence, this suggests that it is not a cluster of stars.
(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 tells us that it could be cluster of stars because they can exist close together (because they do exist even closer together in another galaxy) without being torn apart.
(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 says that it could be a cluster of stars because their gravitational pull would be sufficient.
Answer (B)
Vatsal7794
23 May 2023, 21:47
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Hi Experts
GMATNinja KarishmaB MartyTargetTestPrep and other experts
Can anyone please explain me que 2 option B
"Evidence used to argue for the existence of black holes is indirect, coming from their presumed effects on other astronomical bodies.
"
Which evidence are we talking about and what are the presumed effects?
GMATNinja KarishmaB MartyTargetTestPrep and other experts
Can anyone please explain me que 2 option B
"Evidence used to argue for the existence of black holes is indirect, coming from their presumed effects on other astronomical bodies.
"
Which evidence are we talking about and what are the presumed effects?
23 May 2023, 22:58
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Vatsal7794
This is what the passage gives us:
Astronomers must infer the existence of black holes, which are invisible, from their gravitational influence on the visible bodies surrounding them. 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 of mass at the galaxy’s center is a black hole whose gravity is causing the gas to whirl.
How are we able to see objects? Because they bounce back some part of the light that hits them. Black holes are invisible because they do not bounce back any light; they absorb all of it. Then how do you know that a black hole exists if you can't see it through the telescope? You infer that there is something very dense at the centre by looking at the behaviour of the visible bodies around it. Our sun is at the centre of our solar system and all planets revolve around it. We know why the planets are revolving around the centre - because of sun's gravity.
Now when we see bodies revolving around a centre and at high speeds, we know that there must be something there with very high gravitational force which is keeping the bodies revolving around it. But since we can't see anything at the centre, we assume that it must be a "black hole."
