• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• 5 Day FREE Trial
Study Smarter, Not Harder

Available with Beat the GMAT members only code

• Free Veritas GMAT Class
Experience Lesson 1 Live Free

Available with Beat the GMAT members only code

• 1 Hour Free
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• FREE GMAT Exam
Know how you'd score today for $0 Available with Beat the GMAT members only code • Award-winning private GMAT tutoring Register now and save up to$200

Available with Beat the GMAT members only code

• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• Free Trial & Practice Exam
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• Free Practice Test & Review
How would you score if you took the GMAT

Available with Beat the GMAT members only code

## RC OG 13(After the evidence obtained)

This topic has 1 expert reply and 0 member replies
gocoder Master | Next Rank: 500 Posts
Joined
05 Dec 2015
Posted:
120 messages
Target GMAT Score:
720

#### RC OG 13(After the evidence obtained)

Thu Nov 24, 2016 9:51 am
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.

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.

### GMAT/MBA Expert

DavidG@VeritasPrep Legendary Member
Joined
14 Jan 2015
Posted:
2667 messages
Followed by:
120 members
1153
GMAT Score:
770
Fri Nov 25, 2016 8:04 am
gocoder wrote:
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.

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.

Much of this passage is about the concentration of luminous v nonluminous (dark) matter in the universe.

Paragraph 2, boiled way down, tell us this: researchers have concluded that there is a great deal of nonluminous (dark) matter in spiral galaxies. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous
mass.

So spiral galaxies have lots of nonluminous matter. The claim in lines 34-37 is that as much as 90% of the universe's mass is nonluminous. This makes sense if the composition of spiral galaxies is representative of the composition of all galaxies in the universe.

Now look at answer choice A: Spiral galaxies are less common than types of
galaxies that contain little nonluminous matter.

Well, if there are other, more common, galaxies that have little nonluminous matter, then the conclusion that the universe is mostly nonluminous matter is a good deal weaker. Answer is A

_________________
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save \$100 off any live Veritas Prep GMAT Course

Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!

### Top First Responders*

1 GMATGuruNY 68 first replies
2 Rich.C@EMPOWERgma... 48 first replies
3 Brent@GMATPrepNow 37 first replies
4 Jay@ManhattanReview 26 first replies
5 ErikaPrepScholar 9 first replies
* Only counts replies to topics started in last 30 days
See More Top Beat The GMAT Members

### Most Active Experts

1 GMATGuruNY

The Princeton Review Teacher

128 posts
2 Rich.C@EMPOWERgma...

EMPOWERgmat

117 posts
3 Jeff@TargetTestPrep

Target Test Prep

106 posts
4 Max@Math Revolution

Math Revolution

94 posts
5 Scott@TargetTestPrep

Target Test Prep

92 posts
See More Top Beat The GMAT Experts