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

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Senior Manager
Joined: 04 Sep 2017
Posts: 291
Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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24 Sep 2019, 01:00
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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. 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. 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. 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. 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
Senior Manager
Joined: 04 Sep 2017
Posts: 291
Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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24 Sep 2019, 01:04
2
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.

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. 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. 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. 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

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.
Senior Manager
Joined: 04 Sep 2017
Posts: 291
Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

### Show Tags

24 Sep 2019, 01:08
2
1
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.

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. 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. 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. 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

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.
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Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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03 Nov 2019, 10:53
2

Question #3

3.
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?

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

NoMatterWhat wrote:
UPS67 wrote:
I have issue with the explanation of Question 3.

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

gmat1393 wrote:
Hi GMATNinja

Thanks

Lots of questions on #3! nick1816 and RK007 have it exactly right -- but I'll explain in a bit more depth in case that is helpful to anyone

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

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.

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

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).

Quote:
E. Matter being engulfed by a black hole radiated far more energy than is currently assumed.

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!
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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26 Jan 2020, 23:35
1
Balkrishna wrote:
gmatt1476 wrote:
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.

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. 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. 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. 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

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.

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.

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.
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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24 Sep 2019, 01:06
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.

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. 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. 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. 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

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.
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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24 Sep 2019, 01:10
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.

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. 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. 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. 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

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.
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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24 Sep 2019, 22:58
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.
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Updated on: 30 Sep 2019, 05:42
UPS67 wrote:
I have issue with the explanation of Question 3.

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

Originally posted by NoMatterWhat on 26 Sep 2019, 05:32.
Last edited by NoMatterWhat on 30 Sep 2019, 05:42, edited 1 time in total.
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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29 Sep 2019, 22:38
NoMatterWhat wrote:
UPS67 wrote:
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
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02 Oct 2019, 14:39
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.

UPS67 wrote:
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.
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03 Oct 2019, 09:19
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.
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03 Oct 2019, 14:59
vishumangal
IMO you misunderstood the options given.
If the current assumption is proved to lower, it actually worsen the scenario.

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.

vishumangal wrote:
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.
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03 Oct 2019, 17:02
nick1816 wrote:
vishumangal
IMO you misunderstood the options given.
If the current assumption is proved to lower, it actually worsen the scenario.

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.

vishumangal wrote:
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.

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 ?
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14 Oct 2019, 06:46
UPS67 wrote:
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.

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.
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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19 Oct 2019, 16:53
GMATNinja: For #3, we have problem with less energy radiating.Option E says mote energy is radiated. What is wrong with E.
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22 Oct 2019, 16:25
QUESTION 1: TYPE - PRIMARY PURPOSE QUESTION TYPE

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.

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

RC60500.01-40

Source : Looking Toward a Black Hole Astronomy September 1997

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.
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22 Oct 2019, 16:34
QUESTION 2: TYPE - DETAIL QUESTION TYPE
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.

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

RC60500.01-40[/box_in]

Source : Looking Toward a Black Hole Astronomy September 1997

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

⠀⠀⠀⠀⠀⠀⠀⠀
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22 Oct 2019, 16:45
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!
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Re: Is there a massive black hole at the center of our galaxy, the Milky  [#permalink]

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23 Oct 2019, 12:05
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!
Re: Is there a massive black hole at the center of our galaxy, the Milky   [#permalink] 23 Oct 2019, 12:05

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