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Astronomers theorize that a black hole forms when a massive object 17 Feb 2021, 04:56
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mSKR
Quote:
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?
Quote:
(A) The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
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.

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.

Basically we need to weaken the hypothesis that the concentration in M87 might be a cluster of a billion or so dim stars (Let’s say it cluster theory). In other words, if we can infer that it is black hole then also it undermines the cluster theory.

The last lines of passage says:
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.

It means that starts can be closely spaced due to black hole. If no black hole then cluster would be torn apart

With this understanding when we read A, it says stars could exert a strong gravitational force without tearing cluster apart. So it means it is not due to concentration of billion or so dim stars but because of black hole or other phenomenon; but definitely not due to cluster theory.

With this understanding, why should I not choose A?

Please suggest .

Quote:
(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.

Can I say E supports the conclusion drawn in the last lines of 1st passage instead of weakening? It is actually supporting the cluster theory , is not it? Kindly give your comments.


CrackVerbalGMAT GMATNinja @AndrewN : please give your opinion.
( sorry AndrewN for tagging you again for another passage in a day) :)
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Hello again, mSKR. Both (A) and (E) would strengthen the notion that the whirling gas in M87 could be the result of a cluster of a billion or so dim stars, because each answer choice names a star cluster as the agent that corroborates the astronomical observations. You are correct in saying that you want to weaken the star cluster hypothesis, but you are looking in the wrong place.

Quote:
(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.
Show more
If a star cluster would preclude or rule out the possibility of other established astronomical observations, then we can deduce that a star cluster must not exist at the center of the galaxy, as speculated by a few skeptics. If you did not understand the word preclude, I can see how you would overlook this one, but this answer choice is a clear weakener to what we are being asked about, the star cluster hypothesis.

- Andrew
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Astronomers theorize that a black hole forms when a massive object 18 Feb 2021, 05:02
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mSKR
Quote:
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?
Quote:
(A) The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
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.

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.

Basically we need to weaken the hypothesis that the concentration in M87 might be a cluster of a billion or so dim stars (Let’s say it cluster theory). In other words, if we can infer that it is black hole then also it undermines the cluster theory.

The last lines of passage says:
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.

It means that starts can be closely spaced due to black hole. If no black hole then cluster would be torn apart

With this understanding when we read A, it says stars could exert a strong gravitational force without tearing cluster apart. So it means it is not due to concentration of billion or so dim stars but because of black hole or other phenomenon; but definitely not due to cluster theory.

With this understanding, why should I not choose A?

Please suggest .

Quote:
(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.

Can I say E supports the conclusion drawn in the last lines of 1st passage instead of weakening? It is actually supporting the cluster theory , is not it? Kindly give your comments.


CrackVerbalGMAT GMATNinja @AndrewN : please give your opinion.
( sorry AndrewN for tagging you again for another passage in a day) :)
Show more

Hi mSKR

You are absolutely correct when you say that we are required to weaken the cluster theory. However, you are incorrect in your assessment of the following:

"It means that starts can be closely spaced due to black hole. If no black hole then cluster would be torn apart"

We are dealing here with two alternate hypotheses which are mutually exclusive ie; it is either a cluster of stars or a black hole. It cannot be that the cluster and black hole both exist and hence "stars can be closely spaced due to black hole" is incorrect.

You are also correct in assessing that option (A) states that a cluster of stars can co-exist. However, the reason that the passage rejects cluster theory is because the stars would rip the cluster itself apart (now, let's call this rip theory). Now, if option (A) is true, rip theory is false and hence cluster theory becomes strengthened, whereas we are required to weaken cluster theory. Therefore, (A) cannot be the correct answer.

You are absolutely correct in the reason for rejecting option (E) - it, too, acts as a strengthener of cluster theory and hence cannot be the correct answer.

Hope this helps.
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Astronomers theorize that a black hole forms when a massive object 09 Nov 2021, 00:45
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mSKR
Quote:
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?
Quote:
(A) The stars in a star cluster at the center of M87 could exert a strong gravitational force without tearing the cluster apart.
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.

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.

Basically we need to weaken the hypothesis that the concentration in M87 might be a cluster of a billion or so dim stars (Let’s say it cluster theory). In other words, if we can infer that it is black hole then also it undermines the cluster theory.

The last lines of passage says:
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.

It means that starts can be closely spaced due to black hole. If no black hole then cluster would be torn apart

With this understanding when we read A, it says stars could exert a strong gravitational force without tearing cluster apart. So it means it is not due to concentration of billion or so dim stars but because of black hole or other phenomenon; but definitely not due to cluster theory.

With this understanding, why should I not choose A?

Please suggest .

Quote:
(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.

Can I say E supports the conclusion drawn in the last lines of 1st passage instead of weakening? It is actually supporting the cluster theory , is not it? Kindly give your comments.


CrackVerbalGMAT GMATNinja @AndrewN : please give your opinion.
( sorry AndrewN for tagging you again for another passage in a day) :)
Hello again, mSKR. Both (A) and (E) would strengthen the notion that the whirling gas in M87 could be the result of a cluster of a billion or so dim stars, because each answer choice names a star cluster as the agent that corroborates the astronomical observations. You are correct in saying that you want to weaken the star cluster hypothesis, but you are looking in the wrong place.

Quote:
(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.
If a star cluster would preclude or rule out the possibility of other established astronomical observations, then we can deduce that a star cluster must not exist at the center of the galaxy, as speculated by a few skeptics. If you did not understand the word preclude, I can see how you would overlook this one, but this answer choice is a clear weakener to what we are being asked about, the star cluster hypothesis.

- Andrew
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dear AndrewN, and other GMATNinja, GMATNinjaTwo, VeritasKarishma,
Quote:
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
Show more
.
if there is only one other galaxy that has been observed to containers clouds whirling about its center as they do about the core of M87, then will D implies this phenomenon is unrepresentative ? then D weakens the possible explanation ?
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Astronomers theorize that a black hole forms when a massive object 09 Nov 2021, 14:26
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zoezhuyan

dear AndrewN, and other GMATNinja, GMATNinjaTwo, VeritasKarishma,
Quote:
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
.
if there is only one other galaxy that has been observed to containers clouds whirling about its center as they do about the core of M87, then will D implies this phenomenon is unrepresentative ? then D weakens the possible explanation ?
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Hello, zoezhuyan. The problem I see with answer choice (D) above is that it does not address the possible explanation in question. Look at the last line of the first paragraph again:

Quote:
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.
Show more
The explanation given is that the concentration [of mass] in M87 might be a cluster of a billion or so dim stars rather than a black hole. You should know from CR that to undermine or weaken an argument or explanation, you need to stick to that exact argument or explanation. Thus, we should be looking for an answer choice that touches on this star cluster hypothesis and diminishes its plausibility. Choice (D) attacks the observation itself—that gas is whirling about the center of the galaxy—and that observation merely serves as a premise for the explanation. In short, choice (D) attacks the wrong target. I have discussed choice (B) more in my earlier post, which you quoted above. I hope that you can appreciate why (D) is NOT the answer, though.

Thank you for thinking to ask.

- Andrew
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Astronomers theorize that a black hole forms when a massive object 27 Feb 2022, 15:17
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How would you guys go about reading a passage like this? On one hand there are too many details and it's supposedly preferable to stick to the MAIN IDEA and STRUCTURE. On the other hand, details are a significant, major part of the passage and it seems almost impossible to read the passage without pausing to think about the details and jot them down.

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Astronomers theorize that a black hole forms when a massive object 27 Feb 2022, 22:08
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HWPO
How would you guys go about reading a passage like this? On one hand there are too many details and it's supposedly preferable to stick to the MAIN IDEA and STRUCTURE. On the other hand, details are a significant, major part of the passage and it seems almost impossible to read the passage without pausing to think about the details and jot them down.

GMATNinja KarishmaB
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HWPO - No need to jot anything down. The passage is a short but dense science passage. Usually, for such short dense passages, a good approach is to read them twice. A second reading helps one understand a lot that one misses in the first read because the topic and logic are unfamiliar. Since the passage is short, it doesn't take a lot of time.
Also, it will be very helpful to familiarise yourself with different topics in science, business, history, economics etc. Put extra efforts in the subjects that are beyond your field of work/interest etc
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Astronomers theorize that a black hole forms when a massive object 25 Apr 2022, 03:52
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GMATNinja KarishmaB

Could you please help with the Generic question I have:-

Considering 4th question as the example:-

4. The passage is primarily concerned with

(A) explaining why a particular phenomenon is so rare

(B) criticizing a method used to gather data about a natural phenomenon

(C) considering possible instances of a particular phenomenon

(D) distinguishing among several different kinds of natural phenomena

(E) questioning a widely accepted explanation for an unusual phenomenon



How will I find the right tone of a passage.
How will I know that the author is criticising(B) or considering(C) or explaining(A)
Is there any key word that can help us understand the tone of passage.
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Astronomers theorize that a black hole forms when a massive object 25 Apr 2022, 04:20
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rsrighosh
GMATNinja KarishmaB

Could you please help with the Generic question I have:-

Considering 4th question as the example:-

4. The passage is primarily concerned with

(A) explaining why a particular phenomenon is so rare

(B) criticizing a method used to gather data about a natural phenomenon

(C) considering possible instances of a particular phenomenon

(D) distinguishing among several different kinds of natural phenomena

(E) questioning a widely accepted explanation for an unusual phenomenon



How will I find the right tone of a passage.
How will I know that the author is criticising(B) or considering(C) or explaining(A)
Is there any key word that can help us understand the tone of passage.
Show more

We cannot rely on keywords to tell us the tone. An explanation passage could use a word of criticism. A consideration passage could explain a particular method etc.
The words after 'criticising' or 'considering' or 'explaining' are important to get the primary purpose.

To get the tone, explanation passage will give you the details of the workings of something (this is how A happens, this is why B happens, and then this happens etc). A criticism will point out the flaws. A cautious optimism will reflect a hopeful attitude toward the future etc.
Note that tone is not reflected in one or two words; it is the way the author handles the subject matter. It is what the author says, not really how he says it since GMAT passages will rarely use intense (positive or negative) words. The words used will be well measured, objective and/or evaluative.
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Astronomers theorize that a black hole forms when a massive object 03 Jul 2022, 02:00
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Dear Experts, @AndewN GMATNinja GMATNinjatwo CrackverbalGMAT

Question no. 3

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?

(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.

Could you pls help why C is incorrect?

In choice (C), The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87
And the passage said : 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.
Even, the NGC 4258 has more closely spaced than are the starts within the core of M87. Then, it would be impossible that M87 contains a cluster of a billion or so dim stars.
Then, it literally undermines.
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Tanchat
Dear Experts, @AndewN GMATNinja GMATNinjatwo CrackverbalGMAT

Question no. 3

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?

(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.

Could you pls help why C is incorrect?

In choice (C), The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87
And the passage said : 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.
Even, the NGC 4258 has more closely spaced than are the starts within the core of M87. Then, it would be impossible that M87 contains a cluster of a billion or so dim stars.
Then, it literally undermines.
Show more
Hello, Tanchat. I seem to have touched on just about every other answer choice in question 3 in earlier posts, but not (C). I am not following the logic at the end of your post. I took the same line of the passage as potential support for the alternative (star cluster) hypothesis. Why? Because if the stars in NGC 4258 are more closely spaced than are the stars within the core of M87, and if the stars within NGC 4258 would be so closely spaced that collisions between individual stars would have long ago torn the cluster apart, then we can infer that a galaxy such as M87—one that contains stars that are spaced farther apart—might not be torn apart by collisions between individual stars. There would be no evidence to challenge the star cluster hypothesis.

Does that make sense?

- Andrew
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Astronomers theorize that a black hole forms when a massive object 03 Jul 2022, 10:30
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Tanchat
Dear Experts, @AndewN GMATNinja GMATNinjatwo CrackverbalGMAT

Question no. 3

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?

(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.

Could you pls help why C is incorrect?

In choice (C), The stars within many existing galaxies, such as NGC 4258, are more closely spaced than are the stars within the core of M87
And the passage said : 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.
Even, the NGC 4258 has more closely spaced than are the starts within the core of M87. Then, it would be impossible that M87 contains a cluster of a billion or so dim stars.
Then, it literally undermines.
Hello, Tanchat. I seem to have touched on just about every other answer choice in question 3 in earlier posts, but not (C). I am not following the logic at the end of your post. I took the same line of the passage as potential support for the alternative (star cluster) hypothesis. Why? Because if the stars in NGC 4258 are more closely spaced than are the stars within the core of M87, and if the stars within NGC 4258 would be so closely spaced that collisions between individual stars would have long ago torn the cluster apart, then we can infer that a galaxy such as M87—one that contains stars that are spaced farther apart—might not be torn apart by collisions between individual stars. There would be no evidence to challenge the star cluster hypothesis.

Does that make sense?

- Andrew
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AndrewN
Thank you so much. I wrongly understood that "more closely spaced" = farther the distance among stars.
Then, The stars in NGC 4258 are more closely spaced than are the stars within the core of M87 doesn't help to undermine.
But if, we changed "more closely spaced than" -> "less closely space than", it would help, right?
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Thank you so much. I wrongly understood that "more closely spaced" = farther the distance among stars.
Then, The stars in NGC 4258 are more closely spaced than are the stars within the core of M87 doesn't help to undermine.
But if, we changed "more closely spaced than" -> "less closely space than", it would help, right?
Show more
Hello again, Tanchat. Yes, if we knew from the answer choice that the stars within M87 were more densely packed (i.e. had less space between each other) than those in NGC 4258, then given the same line from the passage that we both quoted earlier, we could reason that the star cluster hypothesis was less likely. (Note that undermine does not demand irrefutable proof against something.)

Thank you for following up.

- Andrew
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AndrewN
Thank you so much. I wrongly understood that "more closely spaced" = farther the distance among stars.
Then, The stars in NGC 4258 are more closely spaced than are the stars within the core of M87 doesn't help to undermine.
But if, we changed "more closely spaced than" -> "less closely space than", it would help, right?
Hello again, Tanchat. Yes, if we knew from the answer choice that the stars within M87 were more densely packed (i.e. had less space between each other) than those in NGC 4258, then given the same line from the passage that we both quoted earlier, we could reason that the star cluster hypothesis was less likely. (Note that undermine does not demand irrefutable proof against something.)

Thank you for following up.

- Andrew
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AndrewN
Thank you so much. I can eliminate all wrong options A,C,D,E

Can I ask one last question?

In (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.

Does the existence of certain other astronomical phenomena include “BLACK HOLE”?

From the phrase : the existence of certain other astronomical phenomena that have been observed at the center of M87. I’m not sure whether “SO DIM STARS” can be observed or not.

Posted from my mobile device
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Astronomers theorize that a black hole forms when a massive object 03 Jul 2022, 12:09
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AndrewN
Thank you so much. I can eliminate all wrong options A,C,D,E

Can I ask one last question?

In (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.

Does the existence of certain other astronomical phenomena include “BLACK HOLE”?

From the phrase : the existence of certain other astronomical phenomena that have been observed at the center of M87. I’m not sure whether “SO DIM STARS” can be observed or not.
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All right, last one. In the context of the sentence, certain other astronomical phenomena that have been observed refers to known or established phenomena. We cannot pick and choose which phenomena we want that description to apply to. If there is even a debate about what constitutes the large concentration of mass at the galaxy’s center—a black hole, a star cluster, or some other, unnamed body about which we can only speculate—then we cannot say exactly which phenomena are covered (most likely the whirling gas, since there is no apparent disagreement on this observation), only which ones are not.

- Andrew
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Astronomers theorize that a black hole forms when a massive object 19 Jan 2023, 06:12
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Dear Experts

I couldn't get question 1, 2 and 3 right. I also found it very difficult to understand the answer choices, and the major reason why I found it difficult was because it seemed very technical to me and it puzzled me. Request you to explain the above questions and the right approach for attempting RC questions when the questions seem very technical.

Thankyou
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Astronomers theorize that a black hole forms when a massive object 19 Jan 2023, 22:16
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tanishkamishra
Dear Experts

I couldn't get question 1, 2 and 3 right. I also found it very difficult to understand the answer choices, and the major reason why I found it difficult was because it seemed very technical to me and it puzzled me. Request you to explain the above questions and the right approach for attempting RC questions when the questions seem very technical.

Thankyou
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A fairly technical passage is usually short, so that's the silver lining.
It's a good idea to be well read and it's never too late to start. If you know a bit about the topic at hand, it becomes far easier to understand.



Question 1. 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?


This is what we are given about the skeptics:
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.

Many astronomers believe that it is a black hole at the centre of M87 that is causing the gas to swirl around but the skeptics say that it is not necessary. It could be a cluster of stars (not that it is but it could be).
Basically, astronomers say that this is A. But skeptics say that it is not necessary. It could be B too. So the skeptics are not saying that it is not A. They are not saying that it is B. They are just saying that either is possible.

(A) The speed of the gas whirling around the center of M87 is caused by a dense object that is not a black hole.

They don't say that it is not a black hole. They say that it is not necessarily a black hole. It could be a black hole or it could be something else too.

(B) The concentration of mass at the center of M87 is probably a large cluster of dim stars.

They don't say that it is a large cluster of dim stars. They say that it could be. It is one of the possible explanations for the gas swirling as is a black hole. Basically there is something with heavy mass concentration.

(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.

They say that a black hole is not the only explanation, not that it is the most likely explanation.

(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.

Correct. They do agree that there is large concentration of mass at the core of M87. They just believe that it may not necessarily be because of a black hole. The large concentration of mass could be a cluster of stars too (which is also a large concentration of mass).

(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.

The skeptics believe that it could be a cluster of stars so they believe that the gravitational influence of a star cluster WOULD BE strong enough to account for the speed of the gas whirling.

Answer (D)
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Astronomers theorize that a black hole forms when a massive object Updated on: 19 Jan 2023, 22:27
Originally posted by KarishmaB on 19 Jan 2023, 22:21.
Last edited by KarishmaB on 19 Jan 2023, 22:27, edited 1 time in total.
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2. The passage asserts which of the following about the existence of black holes?

(A) Astronomers first speculated about the existence of black holes when they observed gas whirling around the center of a particular galaxy.

No information is given on when they FIRST speculated about the existence of black holes.

(B) Evidence used to argue for the existence of black holes is indirect, coming from their presumed effects on other astronomical bodies.

Correct.

Second line of the passage:
Astronomers must infer the existence of black holes, which are invisible, from their gravitational influence on the visible bodies surrounding them.

(C) Recent observations of certain astronomical bodies have offered proof.

It is still speculation as per the passage.

(D) A considerable body of evidence suggests the existence of black holes, even though their behavior is not completely consistent with the laws of physics.

We are not given that there is a 'considerable body of evidence' and nothing about the laws of physics.

(E) Many astronomers are skeptical about certain recent evidence that has been used to argue for the existence of black holes.

The passage says that a few astronomer are skeptical. Also, is this recent evidence, we don't know.

Answer (B)
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Astronomers theorize that a black hole forms when a massive object 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)
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Astronomers theorize that a black hole forms when a massive object 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?
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Astronomers theorize that a black hole forms when a massive object 23 May 2023, 22:58
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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?
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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."
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