Is there a massive black hole at the center of our galaxy, the Milky

Official Explanation

RC60500.01-10

1. The primary purpose of the passage is to

A. present several theories that could account for a particular phenomenon
B. argue that a certain question needs to be reframed in light of new evidence
C. resolve an apparent inconsistency between two lines of evidence
D. explain why a certain issue remains unresolved
E. present evidence that calls into question certain assumptions of a current theory

Main idea

Our goal is to determine which of the five options best expresses the primary purpose of the passage. Note that this question regards the topic and how that topic is discussed: the issue that the passage primarily focuses on concerns the mass at the center of our galaxy. The passage primarily aims to explain why the specific nature of that mass had not—at least in 1997, when the passage was written—been adequately understood.


A. While the passage draws upon certain theoretical findings, it does not present multiple theories.

B. The passage suggests that the author is puzzled by the enormous mass at the center of the Milky Way, in light of evidence showing the relatively low level of energy radiating outward. Nevertheless, the passage never attempts to convince us that the question needs to be reframed.

C. The passage describes an apparent inconsistency—or discrepancy—between two lines of evidence but does not seek to resolve that inconsistency.

D. Correct. As indicated above, this choice expresses the primary purpose of the passage; that is, to explain why the nature of the mass at the center of our galaxy was not adequately understood.

E. Although some of the evidence presented may cast doubt on one or more assumptions of a theory that was current when the passage was written, the passage itself is not primarily focused on identifying any such assumptions.

The correct answer is D.

Official Explanation

RC60500.01-20

2. According to the passage, the dynamical evidence referred to in lines 9–10 supports which of the following?

A. Recent assumptions about the velocities of stars
B. Widely held predictions about the amount of matter a black hole will engulf
C. The existence of an extremely dense object at the center of the Milky Way
D. The contention that too much energy is coming from the mass at the Milky Way's galactic center for that mass to be a black hole
E. The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole

Supporting idea

What does the passage claim the dynamical evidence mentioned supports? The passage states that the dynamical evidence argues for an extremely compact object with a mass two to three million times the mass of our Sun at the center of the Milky Way. An extremely compact object with such a mass would, of course, be tremendously dense.

A. The passage in no way suggests that the dynamical evidence mentioned supports assumptions about the velocities of stars. Rather, it states that the assumptions about the velocities of the stars have been “recently confirmed” and that the dynamical evidence is actually based on these assumptions. If the dynamical evidence is a product of these assumptions, then it cannot be used to support them.

B. The passage suggests that the dynamical evidence is consistent with the existence in the Milky Way of an extremely dense object that is likely a black hole. However, the evidence in no way suggests that reliable predictions can be made about how much matter such a hypothetical black hole would engulf.

C. Correct. As indicated above, this refers to the extremely compact object of immense mass; this object would of course be “extremely dense.”

D. This choice presents a suggestion opposite to the information in the passage. The passage suggests that the object at the center of the Milky Way is in fact radiating too little to be easily identifiable as a black hole.

E. The passage acknowledges that the density of the mass at the center of the Milky Way is consistent with the existence of a black hole there. However, the passage further suggests that an unexpectedly small quantity of energy radiating outward from the center of the Milky Way calls this into question.

The correct answer is C.

Official Explanation

RC60500.01-40

4. The “widely held predictions” mentioned in line 25 are predictions about the

A. compactness of objects whose mass is millions of times the mass of our Sun
B. velocities of stars orbiting the galactic center
C. amount of matter swirling around the object at the center of the Milky Way
D. amount of matter falling into a theoretical central black hole
E. amount of energy that should be coming from a black hole at the center of the Milky Way

Evaluation

What do the “widely held predictions” mentioned in the passage's final sentence refer to? Notice that the final sentence of the passage refers to a comparison between two things: the energy coming from the galactic center and the quantity of energy widely predicted to be radiated from matter being engulfed by a black hole. It follows that the best answer should present an option that refers to a predicted quantity of energy.

A. This choice fails to refer to any predicted quantity of energy.

B. This choice fails to refer to any predicted quantity of energy.

C. This choice fails to refer to any predicted quantity of energy.

D. This choice fails to refer to any predicted quantity of energy.

E. Correct. This choice presents the only option that refers to a predicted quantity of energy.

The correct answer is E.

I have issue with the explanation of Question 2.

As you mentioned "However, if it were discovered that the matter engulfed were several thousand times less than previously estimated, the relatively low level of radiated energy observed would no longer seem at odds with the existence of the hypothesized black hole."

A. Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
B. Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low.

So option A is opposite and option B fits in.
Hence, could you please check the option and correct me if my understanding is wrong.

I m with you, I checked on Option B too.....Please someone help us out

I am with both of you
can anyone help us out with question number 3

Matter that is engulfed at the center of the galaxy is thousands times lower than that would engulfed by a black hole (according to current assumption); Hence, if the matter engulfed by the black hole, according to the current assumption, is proved to be way higher than actual one, we can solve the problem. Option A is saying exactly the same.

nick1816
For Question 3
It is written in the passage that "Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a black hole, the relative lack of energy radiating from the galactic center presents a serious problem".

Thus current assumptions states that at the center of galaxy more mass is consumed and less energy is released which is problematic.
Thus B should be the answer as it says if it is proved that less mass is consumed then less energy will be released.

vishumangal
IMO you misunderstood the options given.
If the current assumption is proved to lower, it actually worsen the scenario.

Think about this way-
mass engulfed by a blackhole= \(2*10^6\) Kg/sec
If this number is proved to be 1000 times less, then mass that actually is engulfed by black hole would be \(2*10^6*10^3\)=\(2*10^9\) Kg/sec


mass engulfed at the center is \(2*10^3\) kg/sec

You can clearly see that option B, if true, would worsen the problem.

These numbers are not real though.

And this confuses me. Because if there is a threshold to the amount of mass that can be engulfed as a black hole, then the amount of radiation(energy) coming from the center of the galaxy might be indicating something completely different and not even a black hole.

So under what assumptions are we making the decision that it is a black hole ?

Am i missing something silly here ?

Hello UPS67,
Maybe this will help you- In option A and B they're talking about the 'ASSUMPTION' to be wrong not the actual scenario!
So if the 'ASSUMPTION' is proved to be too high = actual value is less = which is ok with the current scenario of less energy being radiated = less matter getting engulfed.
I hope this helps.

GMATNinja: For #3, we have problem with less energy radiating.Option E says mote energy is radiated. What is wrong with E.

QUESTION 1: TYPE - PRIMARY PURPOSE QUESTION TYPE



You can reach the answer quite quickly from the first two sentences of the passage. (Highlighted in Blue)
Is there a massive black hole at the center of our galaxy, the Milky Way? The evidence is inconclusive.

The passage suggests that the evidence known can't conclude if there's a black hole in the center or not. If you read through the rest of the passage, we never answer that question.
Answer is D

QUESTION 2: TYPE - DETAIL QUESTION TYPE
This means that the answer should be in the passage!




Only Answer Choice C states that there's a large mass in the center of the universe.

E is a tempting answer, but there's nothing in the highlighted part (in the passage) that suggests that the mass is actually a blackhole



⠀⠀⠀⠀⠀⠀⠀⠀

QUESTION 3: TYPE - OUT OF THE BOX THINKING
This means that the answer should be in the passage!



Serious Problem Listed in the passage:
"the relative lack of energy radiating from the galactic center" Leads to => "there is a discrepancy by a factor of a few thousand."

We are trying to resolve this problem:
So if we know that there's a relative lack of energy radiating from the galactic and the discrepancy is by a factor of a few thousand, this means that discrepancy is below the real value.
To compensate that, you need to have the assumption that there's actually more energy radiation (more matter engulfed) emitted from the galactic center than what is originally known

Only A does so, so A is correct!

Uh, I get what you are saying but I still have a different perspective.
Scenario: In the earlier para, it was mentioned that the body is most probably a black hole but it's confusing because it is not emitting as much matter as it should. 'as it should' is basically what the scientists know up till date which is a very high number.

Solution: what happens if this very high number falls? Then there is no discrepancy and they can confidently conclude that it is a black hole.
Hence, Option B seems right to me. Can anyone please help me out?

But when the energy coming from the
(25)  galactic center is compared to widely held predictions
⠀⠀⠀ based on how much matter should be falling into a
⠀⠀⠀ theoretical central black hole, there is a discrepancy
⠀⠀⠀ by a factor of a few thousand.[/box_in]

Although according to
⠀⠀⠀ current theory this makes the mass at the center
(15)  of the galaxy too dense to be anything but a black
⠀⠀⠀ hole, the relative lack of energy radiating from the
⠀⠀⠀ galactic center presents a serious problem.

jsound996 wrote:

[color=#0000ff]QUESTION 3: TYPE - OUT OF THE BOX THINKING
This means that the answer should be in the passage!

gmatt1476 wrote:

This passage is excerpted from material published
in 1997.
⠀⠀⠀⠀⠀⠀⠀⠀Is there a massive black hole at the center of our
⠀⠀⠀ galaxy, the Milky Way? The evidence is inconclusive.
(5)  Just as the Sun's mass can be determined, given
⠀⠀⠀ knowledge of other variables, by the velocity at
⠀⠀⠀ which its planets orbit, the mass at the center of the
⠀⠀⠀ Milky Way can be revealed by the velocities of stars
⠀⠀⠀ and gas orbiting the galactic center. This dynamical
(10)  evidence, based on recently confirmed assumptions
⠀⠀⠀ about the stars' velocities, argues for an extremely
⠀⠀⠀ compact object with a mass two to three million
⠀⠀⠀ times the mass of our Sun. Although according to
⠀⠀⠀ current theory this makes the mass at the center
(15)  of the galaxy too dense to be anything but a black
⠀⠀⠀ hole, the relative lack of energy radiating from the
⠀⠀⠀ galactic center presents a serious problem. A black
⠀⠀⠀ hole's gravity attracts surrounding matter, which
⠀⠀⠀ swirls around the black hole, emitting some energy
(20)  as it is engulfed. Scientists believe that the amount of
⠀⠀⠀ energy that escapes the black hole should be about
⠀⠀⠀ 10 percent of the matter's rest energy (the energy
⠀⠀⠀ equivalent of its mass according to the equation
⠀⠀⠀ E=mc^2). But when the energy coming from the
(25)  galactic center is compared to widely held predictions
⠀⠀⠀ based on how much matter should be falling into a
⠀⠀⠀ theoretical central black hole, there is a discrepancy
⠀⠀⠀ by a factor of a few thousand.

3. The “serious problem” referred to in line 17 could be solved if which of the following were true?

A. Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
B. Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low.
C. The object at the center of the Milky Way turned out to be far more dense than it is currently estimated to be.
D. The object at the center of the Milky Way turned out to be far more massive than it is currently estimated to be.
E. Matter being engulfed by a black hole radiated far more energy than is currently assumed.

RC60500.01-30

Source : Looking Toward a Black Hole Astronomy September 1997

Serious Problem Listed in the passage:
"the relative lack of energy radiating from the galactic center" Leads to => "there is a discrepancy by a factor of a few thousand."

We are trying to resolve this problem:
So if we know that there's a relative lack of energy radiating from the galactic and the discrepancy is by a factor of a few thousand, this means that discrepancy is below the real value.
To compensate that, you need to have the assumption that there's actually more energy radiation (more matter engulfed) emitted from the galactic center than what is originally known

Only A does so, so A is correct!

3. The "serious problem" referred to in line 17 could be solved if which of the following were true?

A. Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high.
B. Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low.
C. The object at the center of the Milky Way turned out to be far more dense than it is currently estimated to be.
D. The object at the center of the Milky Way turned out to be far more massive than it is currently estimated to be.
E. Matter being engulfed by a black hole radiated far more energy than is currently assumed.

Hi,
I am unable to understand why option A is correct and E is not.
"Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a blackhole, the relative lack of energy radiating from the galactic center presents a serious problem."
I don't understand how is A correct. If the amount of matter a black hole would engulf is proved to be several thousand times too high then wouldn't that mean that the black hole should radiate even more energy than it already does. This doesn't solve the serious problem which states that there is a lack of energy radiating from the center.
Whereas E states that far more energy is currently radiated so then the problem of lack of energy radiated from the center will be solved. So shouldn't this be the correct answer?

2. According to the passage, the dynamical evidence referred to in lines 9–10 supports which of the following?

A. Recent assumptions about the velocities of stars
B. Widely held predictions about the amount of matter a black hole will engulf
C. The existence of an extremely dense object at the center of the Milky Way
D. The contention that too much energy is coming from the mass at the Milky Way's galactic center for that mass to be a black hole
E. The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole

I understand why C is the correct answer. But the passage states that “This dynamical evidence, based on recently confirmed assumptions about the stars' velocities, argues for an extremely compact object with a mass two to three million times the mass of our Sun. Although according to current theory this makes the mass at the center of the galaxy too dense to be anything but a blackhole, the relative lack of energy radiating from the galactic center presents a serious problem”
So option E “The conclusion that a compact object of two to three million times the mass of our Sun is too dense to be anything but a black hole” Cant we say that although the lack of energy radiating from the center proves otherwise, the dynamical evidence supports the fact about compact object and hence the current theory that it cannot be anything but a black hole?