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

Question

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.   1 
 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

RC60500.01-10

2 
 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

RC60500.01-20

3 
 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

4 
 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

RC60500.01-40

Source :  Looking Toward a Black Hole   Astronomy  September 1997

GMATNinja · Accepted Answer

Question #3

First, let's look at the ASSUMPTION made by scientists: "Scientists believe that the amount of energy that escapes the black hole should be about 10 percent of the matter's rest energy."

Now let's look at the ACTUAL amount of energy escaping the black hole: "the  relative lack of energy  radiating from the galactic center presents a serious problem... 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."

So, the ACTUAL amount of energy escaping the black hole is significantly  lower  than the amount that scientists believe should be escaping based on their ASSUMPTION.

Stated another way, the amount of energy that scientists ASSUME should be escaping from the black hole is much  higher  than the ACTUAL amount of energy escaping the black hole.

Question #3 asks us to solve this problem.
 
Okay, so according to (A) the scientists' current ASSUMPTION is way too high. What happens if we modify the current assumption to be thousands of times lower than it currently is, as suggested by (A)?

This totally fixes our problem -- the current assumption is much  higher  than the actual value. An assumption of a much  lower  amount of energy escaping the black hole would match the actual observation.

(A) is the correct answer.

If the current assumption is much too low, then we would need to modify it to be  higher  than it currently is.

But wait! The current assumption is  already much higher  than the actual amount of energy escaping the black hole. If we say that the current assumption needs to be higher than it already is, then the gap between the assumption and the actual value will increase -- which is not what we want.

(B) makes our "serious problem" even worse. Eliminate (B).

Again, we are talking about the ASSUMED amount of energy, which was already much higher than the ACTUAL amount of energy being emitted.

(E), if true, means that matter would radiate  far more  energy than is currently assumed -- in other words,  the current assumption is too low .

Just like (B), (E) increases the gap between the too-high assumption and the actual value, which worsens our problem.

(E) is out, and (A) is the answer.

I hope that helps!

gmatt1476 · Answer

Official Explanation

RC60500.01-30

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.

Application

Which one of the five options would, if true, indicate a possible solution to the serious problem referred to? The serious problem is said to arise from the relative lack of energy radiating from the galactic center compared with the expected value if a matter-engulfing black hole were truly at the center of the Milky Way.

According to the passage, the radiated energy turned out to be a few thousand times less than had been expected, on theoretical grounds, to radiate from mass engulfed by the hypothetical black hole. 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. Correct.  Reviewing the assumptions underlying the widely held predictions could lead to revised predictions that harmonize with the observational evidence regarding radiated energy from the galaxy's center.

B. The passage states that the assumed quantity of engulfed matter already seems to be radiating too little; this answer choice would actually make the “serious problem” in the passage worse. That is, assuming that there is actually more engulfed matter with such a small amount of radiation would simply worsen the problem.

C. The passage does not specify what impact a greater-than-estimated density would have on the quantity of energy that is radiated. That is, even if greater mass would change predictions, greater density may not do so.

D. If the object were more massive, then presumably the matter engulfed by this hypothetical more massive black hole would radiate a quantity of energy even greater than the observed quantity. This again would simply make the “serious problem” worse.

E. Given that not enough radiated energy is currently being observed, finding that the matter being engulfed radiates even more energy than expected would make the “serious problem” significantly worse. That is, the relatively low quantity of radiated energy observed would fall even farther short of the quantity expected.

The correct answer is A.

gmatt1476 · Answer

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.

gmatt1476 · Answer

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.

gmatt1476 · Answer

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.

UPS67 · Answer

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.

RK007 · Answer

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.

Jsound996 · Answer

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

Jsound996 · Answer

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

⠀⠀⠀⠀⠀⠀⠀⠀

Jsound996 · Answer

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!

aniket16c · Answer

Even though GMATNinja has explained the solution to Q3 quite clearly, I would like to post a little mathematical view to this question: Let us consider the assumption side of the scientists: Matter's rest energy = E = 1000 Scientists believe the energy radiated should be 10% of rest energy = 0.1 E = 100 Actual observations: The observed energy radiated = Ea = 10 Given condition = Ea << 0.1 E ( 10 << 100) The question is focusing on making changes in the "Assumption" side and not on the observed side. Hence, whatever alterations are to be made will be in E Choice A: Current assumptions about how much matter a black hole would engulf proved to be several thousand times too high Means the scientists assumed that E was too high --> Thus in practical conditions E's value would decrease. Thus 0.1E's value can decrease from 100 to 10-15. Thus now Ea will be closer to 0.1E - Correct Choice B: Current assumptions about how much matter a black hole would engulf proved to be a few thousand times too low. Means the scientists assumed that E was too low. Thus in actual conditions the value of E should be few thousand times --> E will increase from 1000 to 100,000 --> 0.1E --> 10,000 and Ea will remain 10. Thus we see that the difference has increased. - Incorrect Option E: Matter being engulfed by a black hole radiated far more energy than is currently assumed I believe the trick here is to realize that the option is talking about "Assumption" side. Hence, the "Ea" should be kept unaffected and we need to focus only on "E" part. The matter radiated far more energy --> Means instead of 10% the matters releases say 70% energy. Thus the inequality will transform into Ea << 0.7E --> Thus we see that the difference has increased. - Incorrect

Balkrishna · Answer

Hi GMATNinja ,  VeritasKarishma   MartyTargetTestPrep

Statement from the passage:
 But when the energy coming from the 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

According to the passage, there is a  discrepancy  of a factor of few thousands in the light emitted by the center of the galaxy.

According to official explanation, the discrepancy has been interpreted as a shortage of energy.

Can't discrepancy refer to excess of energy too?

Thank you.

KarishmaB · Answer

Yes, discrepancy can be either excess or shortage.

But, the passage clearly mentions on line 16:
... the relative  lack of energy radiating  from the galactic center presents a serious problem.

SanjaySrini · Answer

GMATNinja 
Hi,
I have a question regarding Q3 option D, if the object is much more massive, it could mean it's not a black hole and that clears our problem right?

GMATNinja · Answer

The passage doesn't tell us that there is a limitation on how massive a black hole can be, so we can't assume that a more massive object would not be a black hole. In fact, the passage tells us that the mass at the center of the galaxy is ALREADY "too dense to be anything but a black hole," and increasing the object's mass without increasing its volume would make the object even more dense. At that point the mass would DEFINITELY still be a black hole.

Because we can't assume that a more massive object would not be a black hole, (D) doesn't resolve the "serious problem" mentioned in the passage and is not the correct answer to question 3.

I hope that helps!

ParikshitAgrawal · Answer

Hi Everyone,

Since I can see that the only debatable question here is 3 ( Diya52  ,  gmat1393  ,  legendinthewomb  ), I will straight away reason out the options of Q3.

Pertinent lines from the passage to answer the question: 
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. A black hole's gravity attracts surrounding matter, which swirls around the black hole, emitting some energy 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.

Understanding: 
The author presents an 'evidence' that the mass of the galaxy's center is too dense and amount of energy radiating out is less than expected.  As this is clearly stated as evidence, this cannot be refuted or argued.  Furthermore, they provide a cause behind any radiation of energy, which is a proportional amount of matter being engulfed by galaxy's center. From this, we can easily infer that they had assumed that the mass being engulfed is way much higher.

Working for assumption: 
For clear visualization, let us say that the mass engulfed by the galaxy's center which was assumed by the scientists was 1000 Kgs. Thus, the energy radiation must be nearly equal to the energy of the mass of 10Kgs (say 10X). But they could evidence only proportional to 5 Kgs (say 5X). Thus, there is a lack of energy radiations. Hence, what if the assumed engulfed mass was only 500 Kgs, then the realised values would hold true.

Now, let's move to the answer choices. 
 
A) This is exactly matching our prethinking. 
B) This is complete opposite of our answer. 
(C) and (D) are completely wrong as the mass of galaxy's center is also accounted for. 
E) This is a tricky option too. Many would opt for this that what if the energy for a proportion of particular mass of kgs is higher. However, you should pay attention to what the evidence is indicating. THE ENERGY RADIATED OUT OF THE GALAXY's CENTER WOULD STILL BE LESS THAN WHAT THEY WERE EXPECTING. Here, since there is no indication on amount of mass being engulfed, lets assume energy emitted is 50% of the energy of the mass being engulfed. Then per this option, and per our previous 'working for assumption', for 5X energy emissions observed, the mass being engulfed would be 10 Kgs. But does this give us an explanation to low energy radiation- NO.

Hence, A is the correct choice.

Hope this helps !!

Regards,
Parikshit

KarishmaB · 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

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.

The extract in bold shows you that the dynamical evidence supports that there is an extremely compact object with a mass two to three million times the mass of our Sun at the centre. 
Answer (C)

IT doesn't tell us that the object is a black hole. It is the current theory that says that the object can be nothing but a black hole.

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.

This means that as per current theory it must be a black hole but since there is relative lack of energy radiating, we cannot say whether it is actually a black hole.

zoezhuyan · Answer

GMATNinja ,  GMATNinjaTwo ,  VeritasKarishma ,  AnthonyRitz ,  CJAnish ,  MartyTargetTestPrep , AndrewN , VeritasPrepBrian 
dear experts, 
what makes me confused is I did catch which is actual energy, what is assumed energy.

one said is according to E=mc^2, one said is prediction.

for me, it is theoretical energy if according to E=mc^2, another is prediction. neither is an actual energy.

did I miss something ?

genuinely need your help.

thanks in advance

GMATNinja · Answer

The prediction made by the scientists is the same as the assumed energy. And this prediction is made on the basis of the equation E=mc^2. The passage makes this clear when it says, “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).”
 
In other words, their prediction/assumption is that the energy escaping the black whole should be 10% of the energy given from the equation E=mc^2. So, the energy assumed/predicted  to escape the black hole  is derived from the matter’s rest energy (“theoretical energy”).

The actual energy emitted by the galaxy’s center is mentioned elsewhere. It’s referred to as the “relative lack of energy radiating from the galactic center   presents a serious problem.” This is the energy that, when “compared to widely held predictions”, presents a “discrepancy by a factor of a few thousand.”

I hope that helps!

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

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

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