• Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep

OG After evidence was obtained in the 1920s

This topic has 1 member reply
AbeNeedsAnswers Master | Next Rank: 500 Posts Default Avatar
Joined
02 Jul 2017
Posted:
191 messages
Followed by:
2 members
Thanked:
1 times

OG After evidence was obtained in the 1920s

Post Thu Jul 27, 2017 9:02 pm
Elapsed Time: 00:00
  • Lap #[LAPCOUNT] ([LAPTIME])
    After evidence was obtained in the 1920s that the universe is expanding, it became reasonable to ask: Will the universe continue to expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? It can be calculated that the critical density of matter needed to brake the expansion and “close” the universe is equivalent to three hydrogen atoms per cubic meter. But the density of the observable universe-luminous matter in the form of galaxies-comes to only a fraction of this. If the expansion of the universe is to stop, there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70.

    Our contribution to the search for this “missing matter” has been to study the rotational velocity of galaxies at various distances from their center of rotation. It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler’s law. Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.

    Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth. Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive. While it has not yet been determined whether this mass is sufficient to close the universe, some physicists consider it significant that estimates are converging on the critical value.

    516) The passage is primarily concerned with
    (A) defending a controversial approach
    (B) criticizing an accepted view
    (C) summarizing research findings
    (D) contrasting competing theories
    (E) describing an innovative technique

    517) The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having
    (A) higher rotational velocity and higher luminosity
    (B) lower rotational velocity and higher luminosity
    (C) lower rotational velocity and lower luminosity
    (D) similar rotational velocity and higher luminosity
    (E) similar rotational velocity and similar luminosity

    518) The authors’ suggestion that “as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth” (lines 34-37) would be most weakened if which of the following were discovered to be true?
    (A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
    (B) Luminous and nonluminous matter are composed of the same basic elements.
    (C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
    (D) The density of the observable universe is greater than most previous estimates have suggested.
    (E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

    519) It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?
    (A) Luminosity would be a true indicator of mass.
    (B) Different regions in spiral galaxies would rotate at the same velocity.
    (C) The universe would continue to expand indefinitely.
    (D) The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
    (E) More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.

    520) The authors propose all of the following as possibly contributing to the “missing matter” in spiral galaxies EXCEPT
    (A) massive black holes
    (B) small black holes
    (C) small, dim stars
    (D) massive stars
    (E) large planets

    Q516: C
    Q517: D
    Q518: A
    Q519: C
    Q520: D

    Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums!
    Post Fri Jul 28, 2017 12:41 pm
    Paragraph Tone, and Quick Summary (Ladder):
    1 = Critical mass for universal contraction
    2 =/+ Result of findings: hidden mass increases from center of galaxy (worth a bit of a richer paraphrase since this singular part of the finding is what the whole passage hinges on)
    3 =/+ 90% of mass not detectable. Missing mass might be enough for contraction

    This passage is an example of a scientifically oriented passage. The key to a science passage is to not worry about the technical vocabulary. For example, do you need to know what Kepler's law is to have a masterful understanding of this passage? No, but we do need to understand the gist of the theory at the backbone of the passage, and be able to form a sassy paraphrase. The GMAT is very careful to discuss concepts that can be boiled down to a basic summary. Here, the author is attempting to present the fact that the universe will expand unless there's enough missing matter for it to contract. The passage discusses some findings that support the idea that there's more missing matter and was previously estimated.

    Structurally speaking paragraph 1 is an introduction of the idea of whether there’s enough matter in the universe for the expansion to stop. Paragraph 2 discusses and of course makes the case about the findings (since this paragraph is built by the researchers) the particular research findings by the individual or individuals writing this passage: they were able to take a look at spiral galaxies and realize that the behavior of the rotation of these galaxies is such that there has to be a lot of missing matter that we can't see.

    It's going to be really handy to draw a little picture of what's happening since this description is at the core of the passage, and having a REALLY basic but comfortable understanding of it will be guaranteed to pay off when we move to the
    questions:

    The further away you move from the center of the galaxy it gets dimmer, and of course it's brighter at the center of the galaxy. But what the findings show is that as you move away from the center there’s still a lot of mass.

    Paragraph 3 then takes the findings, and provides some possible things that could account for that mass such as dim stars, black holes (things that we can't see that contain mass) and ties it all together by saying that all of this missing matter might get pretty close to that critical value that would enable the universe to stop expanding. Notice that list of items? That could be fodder for a Detail EXCEPT question.

    516) The passage is primarily concerned with
    (A) defending a controversial approach
    (B) criticizing an accepted view
    (C) summarizing research findings
    (D) contrasting competing theories
    (E) describing an innovative technique

    Type: Passage Purpose
    As we noted, the purpose of this passage is to present new findings that help explore/evaluate a key question. As always, with a clear overall sense of what the author accomplished in the passage, makes Passage Purpose questions some of the quickest to get right on the entire GMAT. Which option nails it here? C. Summarize research findings.
    What controversial approach, let alone defending something that didn’t happen or wasn’t mentioned. Toss it. Totally random.
    No criticism takes place. There’s a broad theoretical question (is there enough mass in the universe to stop the expansion?), but nowhere is any skepticism exhibited.
    D) There aren’t any competing theories in this passage. Thereby, of course, nothing was contrasted.
    E) This is the runner up option. Here is why we have to strike it: 1) we don’t know if the technique is actually innovative, do we? Secondly, is the author actually describing the technique or the findings? The findings. This is a great example as to how a word by word analysis of the options can suddenly make something seemingly similar so radically different, and in the case of E) wrong.

    C

    517) The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having
    (A) higher rotational velocity and higher luminosity
    (B) lower rotational velocity and higher luminosity
    (C) lower rotational velocity and lower luminosity
    (D) similar rotational velocity and higher luminosity
    (E) similar rotational velocity and similar luminosity

    Type: Detail
    As we saw coming, having that clear simple, lean summary of the core of the study’s findings will pay off. I love this question because if you are applying the EMPOWERgmat techniques, it’s so clear and easy, but if any steps are skipped, it burns people so hard. This question is truth mirror. The first reward comes from understanding EXACTLY what the question is asking about: the region near the center of the galaxy (NOT the outermost region). Next, a quick summary before we head to the options. What do we know about the center? It’s brighter, mass roughly similar, and similar rotation. Find that option for me: D. Done. The rest are obvious garbage. The question brutally punishes a huge chunk of people who aren’t careful enough and think they’re being asked about the outer part. B (even though lower rotational velocity is directly contradicted).

    To dismiss all of the other options, let’s revisit our picture. The further away you move from the center of the galaxy it gets dimmer, and of course it's brighter at the center of the galaxy. But what the findings show is that as you move away from the center there’s still a lot of mass.

    D

    518) The authors’ suggestion that “as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth” (lines 34-37) would be most weakened if which of the following were discovered to be true?
    (A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
    (B) Luminous and nonluminous matter are composed of the same basic elements.
    (C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
    (D) The density of the observable universe is greater than most previous estimates have suggested.
    (E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

    Type: Weaken (just like in CR)
    This question is made far easier to tackle once you’re intimate with the 3 Massive CR assumptions: 1) No other factors; 2) Success; 3) Relevance/representativeness. Which one is in full feature here in this argument? Relevance/representativeness. How so? This whole argument rests on the sample used in this research. Let’s check out our options.

    Bingo! The argument would be devastated if it turned out that spiral galaxies, the type focused on in this research, turned out to be less common than other types of galaxies. That would essentially render this study anything from significantly to severely less significant.
    What luminous and nonluminous matter is composed of has no impact on the argument because the issue is about the brightness (or lack of) of the matter. Totally irrelevant.
    If galactic nuclei contain some nonluminous matter, that in no way has any clear, significant impact on the argument. There could indeed be some nonluminous matter in the nuclei and the argument could still remain exactly as it stands. The argument isn’t saying that the only place nonluminous matter can be found is away from the nucleus.
    This option echoes the very suggestion of the research findings, so that in no way would weaken the suggestion.
    Some is a classic ambiguous GMAT word. “Some” doesn’t automatically make an option wrong, but it should always trigger our skepticism. We’re already told that this study is of spiral galaxies, and from what the passage says and suggests that appears enough to make the author’s case. Whether “some” galaxies (spiral or not) rotate too slowly to be measured is not obviously relevant.

    A

    519) It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?
    (A) Luminosity would be a true indicator of mass.
    (B) Different regions in spiral galaxies would rotate at the same velocity.
    (C) The universe would continue to expand indefinitely.
    (D) The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
    (E) More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.

    Type: Inference
    In paragraph 1, the passage states:
    “It can be calculated that the critical density of matter needed to brake the expansion and “close” the universe is equivalent to three hydrogen atoms per cubic meter.”
    So then, we can infer what would happen if the density were less than 3 hydrogen atoms per cubic meter? The universe would continue to expand. That’s C. Done.
    Let’s disassemble each of the remaining options:
    There’s absolutely no connection between the density of hydrogen atoms and the validity of using luminosity as an indicator of mass. That’s completely random.
    Just like A, this option raises something that has absolutely no connection to the density of hydrogen atoms in the universe. Both of these options are just so random for anyone who EMPOWER read the passage. These options are punishments for skimmers and those intimidated by or uninterested in science.
    D) This option repeats some terms raised in the last sentence of P1, but it miserably botches it. The last sentence of P1 tells us that for the universe to stop expanding, there would have to be 70x the nonluminous matter. That’s the condition for the universe to stop expanding, but the question is referring to a condition when the universe doesn’t have enough matter to stop expanding (and thus keeps expanding). Two radically different scenarios.
    E) This option is weird. It’s suggesting that there’s something compelling scientists to locate this matter. In addition, if there were fewer than 3 hydrogen atoms per cubic meter, there’s no clear connection to where in a spiral galaxy whatever nonluminous matter there happened to be.

    C

    520) The authors propose all of the following as possibly contributing to the “missing matter” in spiral galaxies EXCEPT
    (A) massive black holes
    (B) small black holes
    (C) small, dim stars
    (D) massive stars
    (E) large planets

    Type: Detail EXCEPT
    As is the tradition with Detail EXCEPT questions, it draws from a list. This time it’s the list presented in P3 about what forms that nonluminous matter might take:
    extremely dim stars of low mass
    large planets like Jupiter
    small black holes
    massive black holes
    Which option defies that list?

    D.

    Best Conversation Starters

    1 LUANDATO 157 topics
    2 lheiannie07 87 topics
    3 Roland2rule 75 topics
    4 ardz24 64 topics
    5 AAPL 58 topics
    See More Top Beat The GMAT Members...

    Most Active Experts

    1 image description EconomistGMATTutor

    The Economist GMAT Tutor

    163 posts
    2 image description GMATGuruNY

    The Princeton Review Teacher

    133 posts
    3 image description Jay@ManhattanReview

    Manhattan Review

    128 posts
    4 image description Rich.C@EMPOWERgma...

    EMPOWERgmat

    121 posts
    5 image description Brent@GMATPrepNow

    GMAT Prep Now Teacher

    100 posts
    See More Top Beat The GMAT Experts