Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized for You
we will pick new questions that match your level based on your Timer History
Track Your Progress
every week, we’ll send you an estimated GRE score based on your performance
Practice Pays
we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
Your score will improve and your results will be more realistic
Is there something wrong with our timer?Let us know!
Is there a massive black hole at the center of our galaxy, the Milky
[#permalink]
20 Sep 2021, 05:37
Expert Reply
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
A
B
C
D
E
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.
Question 1
00:00
A
B
C
D
E
Question Stats:
71% (02:05) correct
29% (02:20) wrong based on 21 sessions
HideShow
timer Statistics
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
Question 2
00:00
A
B
C
D
E
Question Stats:
61% (01:39) correct
39% (01:42) wrong based on 18 sessions
HideShow
timer Statistics
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
Question 3
00:00
A
B
C
D
E
Question Stats:
36% (01:17) correct
64% (01:23) wrong based on 14 sessions
HideShow
timer Statistics
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.
Question 4
00:00
A
B
C
D
E
Question Stats:
60% (00:52) correct
40% (00:45) wrong based on 10 sessions
HideShow
timer Statistics
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
Re: Is there a massive black hole at the center of our galaxy, the Milky
[#permalink]
02 Oct 2021, 00:17
3
Expert Reply
Official Explanation
3. The “serious problem” referred to in line 17 could be solved if which of the following were true?
Difficulty Level: Very Hard
Explanation
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.
Re: Is there a massive black hole at the center of our galaxy, the Milky
[#permalink]
02 Oct 2021, 00:19
2
Expert Reply
Official Explanation
4. The “widely held predictions” mentioned in line 25 are predictions about the
Difficulty Level: Medium
Explanation
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.
gmatclubot
Re: Is there a massive black hole at the center of our galaxy, the Milky [#permalink]