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. 1 91. 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. 2 92. 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. 3 93. 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 4 94. 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 5 95. 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 6 96. 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. 7 97. 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

Last visit was: 21 Apr 2026, 07:32

It is currently 21 Apr 2026, 07:32

Toolkit

Reading Comprehension (RC)

GMAT Club Daily Prep

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 GMAT 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.

Go to My Error Log Learn more

Request Expert Reply

Confirm Cancel

Apr 16
Sneak Peek: $200 Off GMAT Prep
12:00 PM EDT
-
11:59 PM EDT
You’re first to know: Save $200 on GMAT prep starting tomorrow, 4/13. Get 6 official practice tests and study with real questions. Be ready to save!
Apr 26
Score High on the GMAT with Target Test Prep
10:00 AM EDT
-
11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 27
Try OnDemand GMAT Masterclass
11:00 AM EDT
-
12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 28
Join - GMAT Day!
08:00 AM PDT
-
11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.

Back to Forum

Create Topic

In addition to conventional galaxies, the universe contains very dim

1 2

GMATCoachBen

Tutor

Joined: 21 Mar 2017

Last visit: 11 Apr 2026

Posts: 463

Own Kudos:

3,059

[1]

Given Kudos: 215

Status:Professional GMAT Trainer

Affiliations: GMAT Coach

Location: United States (WA)

GMAT Focus 1: 775 Q87 V90 DI88 (Online) Verified score

GMAT 1: 760 Q50 V44 Verified score

GMAT 2: 770 Q51 V44 Verified score

GMAT 3: 770 Q50 V44 Verified score

GMAT 4: 770 Q50 V45 (Online) Verified score

GMAT 5: 780 Q51 V48 Verified score

Expert

Expert reply

GMAT Focus 1: 775 Q87 V90 DI88 (Online) Verified score

GMAT 5: 780 Q51 V48 Verified score

Posts: 463

Kudos: 3,059

[1]

09 Apr 2024, 18:22

Kudos

Bookmarks

Gmatguy007

In the second question (It can be inferred from the passage that which of the following is an accurate physical description of typical low-surface-brightness galaxies?) I chose (A) since in the first paragraph says 'they have far fewer stars per unit volume than do conventional galaxies' and in combination with the fact that they are larger than conventional galaxies I inferred that they have fewer stars in total (for instance 10 stars per unit volume instead of 15, so they have 5 few per unit volume).

Where am I mistaken?? GMATCoachBen GMATNinja avigutman chetan2u

Thanks in advance

Gmatguy007

(A) They are large spiral galaxies containing fewer stars than do conventional galaxies.

2 problems with A:

1) It directly says in lines 4-5:

"these galaxies have the same general shape and even the same approximate number of stars"

2) The 2 facts you cite OFFSET each other:

(Fewer stars per unit volume) * (LARGER volume) = potentially the same number of stars, since these 2 variables could offset each other

In general, we want to get extremely comfortable with all kinds of rates, since these are all over the GMAT; we multiply the rate by the denominator in the rate.

For example:

(Passengers / Flight) * Flights = Passengers

($ / Unit) * Units = $

(Miles / Gallon) * Gallons = Miles

VerbalBot

Non-Human User

Joined: 01 Oct 2013

Last visit: 04 Jan 2021

Posts: 19,403

Own Kudos:

1,009

Posts: 19,403

Kudos: 1,009

18 Apr 2026, 19:39

Kudos

Bookmarks

Automated notice from GMAT Club VerbalBot:

A member just gave Kudos to this thread, showing it’s still useful. I’ve bumped it to the top so more people can benefit. Feel free to add your own questions or solutions.

This post was generated automatically.

1 2

Moderators:

GMATNinja

GMAT Club Verbal Expert

7391 posts

AbhishekP220108

494 posts

bhanu29

358 posts