Reading Passage Question
In addition to conventional galaxies, the universe contains very dim galaxies that until recently went unnoticed by astronomers. Possibly as numerous as conventional galaxies, these galaxies have the same general shape and even the same approximate number of stars as a common type of conventional galaxy, the spiral, but tend to be much larger. Because these galaxies’ mass is spread out over larger areas, they have far fewer stars per unit volume than do conventional galaxies. Apparently these low-surface-brightness galaxies, as they are called, take much longer than conventional galaxies to condense their primordial gas and convert it to stars—that is, they evolve much more slowly.
These galaxies may constitute an answer to the long-standing puzzle of the missing baryonic mass in the universe. Baryons—subatomic particles that are generally protons or neutrons—are the source of stellar, and therefore galactic, luminosity, and so their numbers can be estimated based on how luminous galaxies are. However, the amount of helium in the universe, as measured by spectroscopy, suggests that there are far more baryons in the universe than estimates based on galactic luminosity indicate. Astronomers have long speculated that the missing baryonic mass might eventually be discovered in intergalactic space or as some large population of galaxies that are difficult to detect.
“In addition to conventional galaxies, the universe contains very dim galaxies” - is a GMAT reading comprehension passage with answers. Candidates need a strong knowledge of English GMAT reading comprehension.
This GMAT Reading Comprehension consists of 7 comprehension questions. The GMAT Reading Comprehension questions are designed for the purpose of testing candidates’ abilities in understanding, analyzing, and applying information or concepts. Candidates can actively prepare with the help of GMAT Reading Comprehension Practice Questions.
Solution and Explanation
- According to the passage, conventional spiral galaxies differ from low-surface-brightness galaxies in which of the following ways?
(A) They have fewer stars than do low-surface brightness galaxies.
(B) They evolve more quickly than low-surfacebrightness galaxies.
(C) They are more diffuse than low-surface brightness galaxies.
(D) They contain less helium than do low-surface brightness galaxies.
(E) They are larger than low-surface-brightness galaxies.
Answer: B
Explanation: We can understand from the passage that dim galaxies take longer than conventional galaxies to convert their primordial gasses into stars. This means that dim galaxies evolve much more slowly than conventional galaxies. The same is stated in option B, making it the correct choice.
- It can be inferred from the passage that which of the following is an accurate physical description of typical low-surface-brightness galaxies?
(A) They are large spiral galaxies containing fewer stars than do conventional galaxies.
(B) They are compact but very dim spiral galaxies.
(C) They are diffuse spiral galaxies that occupy a large volume of space.
(D) They are small, young spiral galaxies that contain a high proportion of primordial gas.
(E) They are large, dense spirals with low luminosity.
Answer: C
Explanation: The passage states that dim galaxies tend to be much larger and spread out over larger areas of space than conventional galaxies.We can easily say that C is the correct answer.
- It can be inferred from the passage that the “longstanding puzzle” refers to which of the following?
(A) The difference between the rate at which conventional galaxies evolve and the rate at which low-surface-brightness galaxies evolve
(B) The discrepancy between estimates of total baryonic mass derived from measuring helium and estimates based on measuring galactic luminosity
(C) The inconsistency between the observed amount of helium in the universe and the number of stars in typical low-surface-brightness galaxies
(D) Uncertainties regarding what proportion of baryonic mass is contained in intergalactic space and what proportion in conventional galaxies
(E) Difficulties involved in detecting very distant galaxies and in investigating their luminosity
Answer: B
Explanation: As per the passage, the puzzle is that spectroscopic measurement of helium in the universe suggests that the baryonic mass is much higher than indicated by measurement of luminosity. The measurements using spectroscopy and measurements using luminosity show a difference in estimate of the mass. Hence, B is the correct answer.
- The author implies that low-surface-brightness galaxies could constitute an answer to the puzzle discussed in the second paragraph primarily because
(A) they contain baryonic mass that was not taken into account by researchers using galactic luminosity to estimate the number of baryons in the universe
(B) they, like conventional galaxies that contain many baryons, have evolved from massive, primordial gas clouds
(C) they may contain relatively more helium, and hence more baryons, than do galaxies whose helium content has been studied using spectroscopy
(D) they have recently been discovered to contain more baryonic mass than scientists had thought when low-surface-brightness galaxies were first observed
(E) they contain stars that are significantly more luminous than would have been predicted on the basis of initial studies of luminosity in lowsurface-brightness galaxies
Answer: A
Explanation: The passage states that astronomers did not notice dim galaxies until recently. These galaxies may help them find the missing baryonic mass. The passage also suggests that astronomers measure the luminosity of specific galaxies .So we can understand that prior to their being noticed by astronomers, the luminosity of these dim galaxies was not measured. Also, their baryonic mass was not taken into account in the estimates of luminosity which led to the long-standing puzzle. Hence, A is the correct answer.
- The author mentions the fact that baryons are the source of stars’ luminosity primarily in order to explain
(A) how astronomers determine that some galaxies contain fewer stars per unit volume than do others
(B) how astronomers are able to calculate the total luminosity of a galaxy
(C) why astronomers can use galactic luminosity to estimate baryonic mass
(D) why astronomers’ estimates of baryonic mass based on galactic luminosity are more reliable than those based on spectroscopic studies of helium
(E) how astronomers know bright galaxies contain more baryons than do dim galaxies
Answer: C
Explanation: The passage explains that scientists have been puzzled over missing baryonic mass in the universe which was measured by luminosity. If we consider baryons as the source of luminosity in the galaxy, astronomers can estimate the baryonic mass of a galaxy by measuring its luminosity. Hence, the passage indicates that because baryons are the source of galactic luminosity, measuring luminosity can be used to estimate baryonic. Hence, C is the correct answer.
- The author of the passage would be most likely to disagree with which of the following statements?
(A) Low-surface-brightness galaxies are more difficult to detect than are conventional galaxies.
(B) Low-surface-brightness galaxies are often spiral in shape.
(C) Astronomers have advanced plausible ideas about where missing baryonic mass might be found.
(D) Astronomers have devised a useful way of estimating the total baryonic mass in the universe.
(E) Astronomers have discovered a substantial amount of baryonic mass in intergalactic space.
Answer: E
Explanation: The second paragraph indicates that astronomers have estimated the baryonic mass of the universe. The last sentence states that astronomers have speculated that the missing baryonic mass might be discovered in intergalactic space. The passage does not provide any such information that baryonic mass has been discovered in intergalactic space. Hence, E is the correct answer.
- The primary purpose of the passage is to
(A) describe a phenomenon and consider its scientific significance
(B) contrast two phenomena and discuss a puzzling difference between them
(C) identify a newly discovered phenomenon and explain its origins
(D) compare two classes of objects and discuss the physical properties of each
(E) discuss a discovery and point out its inconsistency with existing theory
Answer: A
Explanation: We can see that the first paragraph talks about the phenomenon of the discovery of dim galaxies and some of their general attributes. The next paragraph states how this discovery might assist astronomers to solve a puzzle about the baryonic mass of the universe. The scientific significance is considered. Hence, A is the correct answer.
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