The discoveries of the white dwarf, the neutron star, and the black

Question

The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the red giant are among the most exciting developments in decades because they may be well present physicists with their greatest challenge since the failure of classical mechanics. In the life cycle of the star, after all of the hydrogen and helium fuel has been burned, the delicate balance between the outer nuclear radiation pressure and the stable gravitational force becomes disturbed and slow contraction begins. As compression increases, a very dense plasma forms. If the initial star had mass of less than 1.4 solar masses (1.4 times the mass of our sun), the process ceases at the density of 1,000 tons per cubic inch, and the star becomes the white dwarf. However, if the star was originally more massive, the white dwarf plasma can’t resist the gravitational pressures, and in rapid collapse, all nuclei of the star are converted to a gas of free neutrons. Gravitational attraction compresses this neutron gas rapidly until a density of 10 tons per cubic inch is reached; at this point the strong nuclear force resists further contraction. If the mass of the star was between 1.4 and a few solar masses, the process stops here, and we have a neutron star.

But if the original star was more massive than a few solar masses, even the strong nuclear forces cannot resist the gravitational crunch. The neutrons are forced into one another to form heavier hadrons and these in turn coalesce to form heavier entities, of which we as yet know nothing. At this point, a complete collapse of the stellar mass occurs; existing theories predict a collapse to infinite density and infinitely small dimensions Well before this, however, the surface gravitational force would become so strong that no signal could ever leave the star - any photon emitted would fall back under gravitational attraction – and the star would become black hole in space.

This gravitational collapse poses a fundamental challenge to physics. When the most widely accepted theories predict such improbable things as infinite density and infinitely small dimensions, it simply means that we are missing some vital insight. This last happened in physics in the 1930’s, when we faced the fundamental paradox concerning atomic structure. At that time, it was recognized that electrons moved in table orbits about nuclei in atoms. However, it was also recognized that if charge is accelerated, as it must be to remain in orbit, it radiates energy; so, theoretically, the electron would be expected eventually to spiral into the nucleus and destroy the atom. Studies centered around this paradox led to the development of quantum mechanics. It may well be that an equivalent t advance awaits us in investigating the theoretical problems presented by the phenomenon of gravitational collapse.

1. The primary purpose of the passage is to

A. offer new explanations for the collapse of stars.
B. explain the origins of black holes, neutron stars, and white dwarfs.
C. compare the structure of atoms with the structure of the solar system.
D. explain how the collapse of stars challenges accepted theories of physics.
E. describe the imbalance between radiation pressure and gravitational force.

2. According to the passage, in the final stages of its development our own sun is likely to take the form of a

A. white dwarf
B. neutron star
C. red giant
D. gas of free neutrons
E. black hole

3. According to the passage, an imbalance arises between nuclear radiation pressure and gravitational force in stars because

A. the density of a star increases as it ages
B. radiation pressure increases as a star increases in mass
C. radiation pressure decreases when a star’s fuel has been consumed
D. the collapse of a star increases its gravitational force.
E. a dense plasma decreases the star’s gravitational force.

4. The author asserts that the discoveries of the white dwarf, the neutron star, and the black hole are significant because these discoveries.

A. demonstrate the probability of infinite density and infinitely small dimensions
B. pose the most comprehensive and fundamental problem faced by physicists in decades
C. clarify the paradox suggested by the collapse of electrons into atomic nuclei.
D. establish the relationship between the mass and gravitational pressure.
E. assist in establishing the age of the universe by tracing the life histories of stars.

5. The passage contains information that answers which of the following questions?

I. What is the density limit of the gravitational collapse of neutron stars?
II. At what point in its life cycle does a star begin to contract?
III . What resists the gravitational collapse of a star?

A. I only
B. III only
C. I and II only
D. II and III only
E. I, II, and III

6. The author introduces the discussion of the paradox concerning atomic structures(in highlighted text) in order to

A. Show why it was necessary to develop quantum mechanics
B. Compare the structure of an atom with the structure of star
C. Demonstrate by analogy that a vital insight in astrophysics is missing
D. Illustrate the contention that improbable things do happen in astrophysics
E. Argue that atoms can collapse if their electrons do not remain in orbit.

7. According to the passage, paradoxes are useful in a scientific investigation because they

(A) point to the likelihood of impending discoveries
(B) assist scientists in making comparisons with other branches of knowledge
(C) disprove theories that have been called into question
(D) call attention to inadequacies of existing theory
(E) suggest new hypotheses that can be tested by observation

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JOURNAL ARTICLE
New Directions in Physics: Man's understanding of his universe and his technological abilities to satisfy his needs are undergoing major change because of new discoveries in all branches of physics
D. Allan Bromley
American Scientist
Vol. 62, No. 3 (May-June 1974), pp. 293-303
Published by: Sigma Xi, The Scientific Research Honor Society
https://www.jstor.org/stable/27844883
Page Count: 11

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File comment: New Directions in Physics: Man's understanding of his universe and his technological abilities to satisfy his needs are undergoing major change because of new discoveries in all branches of physics

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Show Answer Question #1

Official Answer

D

Show Answer Question #2

Official Answer

A

Show Answer Question #3

Official Answer

C

Show Answer Question #4

Official Answer

B

Show Answer Question #5

Official Answer

E

Show Answer Question #6

Official Answer

C

Show Answer Question #7

Official Answer

D

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Nikhil · Accepted Answer

1. The primary purpose of the passage is to

A. offer new explanations for the collapse of stars.
B. explain the origins of black holes, neutron stars, and white dwarfs.
C. compare the structure of atoms with the structure of the solar system.
 D. explain how the collapse of stars challenges accepted theories of physics. 
E. describe the imbalance between radiation pressure and gravitational force.

The best answer is D. The central idea of the passage is that the final possible stage in the gravitational collapse of a star, a black hole, produces a state of affairs in which' 'widely accepted theories predict. . . improbable things" (lines 44-45). This situation, the author points out, "may well present physicists with their greatest challenge" since the failure of classical physics (lines 5-6) and' 'poses a fundamental challenge to physics" (lines 43-44). The idea of the challenge is reinforced by the analogy drawn between this situation in physics and the atomic structure paradox of the 1930s. Thus the whole purpose of the passage is to explain the process of gravitational collapse and to suggest how this challenges accepted theories in physics.

2. According to the passage, in the final stages of its development our own sun is likely to take the form of a

A. white dwarf 
B. neutron star
C. red giant
D. gas of free neutrons
E. black hole

The best answer is A because lines 12-16 indicate that all stars with a mass less than 1.4 times the mass of our sun will collapse into white dwarfs. As our sun fits this condition, it must eventually collapse into a white dwarf.

3. According to the passage, an imbalance arises between nuclear radiation pressure and gravitational force in stars because

A. the density of a star increases as it ages
B. radiation pressure increases as a star increases in mass
 C. radiation pressure decreases when a star’s fuel has been consumed 
D. the collapse of a star increases its gravitational force.
E. a dense plasma decreases the star’s gravitational force.

The best answer is C because lines 7-11 indicate that a disturbance in the balance between outward nuclear radiation and stable inward gravitational force occurs "after all of the hydrogen and helium fuel has been burned." Since "slow contraction begins" after the fuel is consumed, and since the gravitational force is stable, the imbalance must be caused by a lessening in the outward radiation pressure.

4. The author asserts that the discoveries of the white dwarf, the neutron star, and the black hole are significant because these discoveries.

A. demonstrate the probability of infinite density and infinitely small dimensions
 B. pose the most comprehensive and fundamental problem faced by physicists in decades 
C. clarify the paradox suggested by the collapse of electrons into atomic nuclei.
D. establish the relationship between the mass and gravitational pressure.
E. assist in establishing the age of the universe by tracing the life histories of stars.

The best answer is B. Lines 1-6 state that the discoveries of the white dwarf, the neutron star, and the black hole are among the most exciting developments in recent physics and " may well present physicists with their greatest challenge since the failure of classical mechanics." This "challenge" is explained in the rest of the passage, where it is described as "fundamental" (line 43), as being of a magnitude that was last seen in physics "in the 1930's" (lines 48-49), and as conceivably leading to an advance the equivalent of the development of quantum mechanics (lines 57-61). Thus the author considers the discoveries significant because they pose problems of a magnitude that physics has not seen since the 1930s.

5. The passage contains information that answers which of the following questions?
I. What is the density limit of the gravitational collapse of neutron stars?
II. At what point in its life cycle does a star begin to contract?
III . What resists the gravitational collapse of a star?

A. I only
B. III only
C. I and II only
D. II and III only
 E. I, II, and III

The best answer is E. Question I is answered in lines 21-23, where it is stated that in the case of neutron stars, gravitational compression continues until a density of 10 tons per cubic inch is reached. Question II is answered in lines 7-11, where it is stated that stars begin to contract after all hydrogen and helium fuel has been burned. Question III has three answers, depending on what stage a star is in. First, outward nuclear radiation resists gravitational collapse (lines 8-10); next the white dwarf plasma resists gravitational collapse (lines 18-19), and finally, the strong nuclear force resists gravitational collapse (lines 21-24). Thus all three questions are answered in the passage and E is the correct choice.

6. The author introduces the discussion of the paradox concerning atomic structures(in highlighted text) in order to

A. Show why it was necessary to develop quantum mechanics
B. Compare the structure of an atom with the structure of a star
 C. Demonstrate by analogy that a vital insight in astrophysics is missing 
D. Illustrate the contention that improbable things do happen in astrophysics
E. Argue that atoms can collapse if their electrons do not remain in orbit.

The best answer is C. In lines 44-48 the author introduces the discussion of the atomic structure paradox by noting that when improbable things happen it means that physicists "are missing some vital insight." The author then states that' 'This last happened in physics in the 1930s, when we faced a fundamental paradox concerning atomic structure" (lines 48- 50). The author closes the discussion by suggesting "that an equivalent advance awaits us" (line 59) in astrophysics. Together these imply that the author sees an analogy between the atomic structure paradox and the gravitational collapse problem in astrophysics, and anticipates that the second will be solved in the same way as the first, by a new vital insight.

7. According to the passage, paradoxes are useful in scientific investigation because they 
(A) point to the likelihood of impending discoveries 
(B) assist scientists in making comparisons with other branches of knowledge
(C) disprove theories that have been called into question
 (D) call attention to inadequacies of existing theory 
(E) suggest new hypotheses that can be tested by observation

The best answer is D. Two paradoxes are described in the passage, the atomic structure problem of the 1930s and the gravitational collapse problem, and both are depicted as calling attention to problems in existing scientific theories. In lines 57-58 the author notes that work in atomic structure physics focused on the inconsistencies of the existing theories, and in lines 44-48 that the discoveries of such paradoxical phenomena as infinite density and infinitely small dimensions tell physicists that "some vital insight" is missing within the existing theory. Thus in both cases, the paradoxes serve to point out problems with existing theories and to draw the attention of physicists toward solving them.

GMATNinja · Answer

Pay close attention to the wording of question 7:

We need an answer choice that represents a reason why paradoxes are USEFUL in scientific investigation. Now consider choice (A):

First, the passage doesn't exactly imply that this is true. Paradoxes can present scientists with great challenges, but that does not necessarily mean that the scientists will be able to  resolve  those paradoxes. And that certainly does not necessarily mean that those paradoxes will be resolved any time soon or that discoveries are about to happen ( impending ). The passage suggests that paradoxes can lead to exciting scientific challenges. But the  creation  of a new scientific challenge does not, by itself, imply that we are on the verge of new discoveries.

Second, even if we assume that a paradox is a sign of impending discoveries, does that make the paradox  useful  in scientific investigation? Does the knowledge that new discoveries are on the way actually  help  scientific investigation? Sure, maybe scientists get excited about the new challenge and become motivated to make scientific progress... but that's not WHY the paradoxes themselves are useful according to the passage.

The paradoxes themselves are  useful  because they expose the flaws of existing theories. The paradoxes tell us exactly  what  is wrong and thus tell us what we need to address. Knowing what is wrong with existing theories is a huge step towards scientific progress, and that makes the paradoxes themselves useful in a scientific investigation.

(D) is a better choice than (A).

I hope this helps!

Skywalker18 · Answer

Interesting read, all correct in 10 mins, including almost 5 mins to read.
Para 1- discoveries of white dwarf, the neutron star, and the black hole etc and how two of them are formed
Para 2- an extension of para 1 to describe black hole formation
Para 3- analogy using quantum mechanics interpretation of classical mechanics' explanation of atomic structure

1. The primary purpose of the passage is to

A. offer new explanations for the collapse of stars. - Incorrect - no new explanations are provided
B. explain the origins of black holes, neutron stars, and white dwarfs. - Incorrect
C. compare the structure of atoms with the structure of the solar system. - Incorrect - no such comparison is made
D. explain how the collapse of stars challenges accepted theories of physics. - Correct - 
E. describe the imbalance between radiation pressure and gravitational force. - Incorrect - this is just a reason as to why stars begin to contract

2. According to the passage, in the final stages of its development our own sun is likely to take the form of a

A. white dwarf - Correct - If the initial star had mass of less than 1.4 solar masses (1.4 times the mass of our sun), the process ceases at the density of 1,000 tons per cubic inch, and the star becomes the white dwarf.

3. According to the passage, an imbalance arises between nuclear radiation pressure and gravitational force in stars because

C. radiation pressure decreases when a star’s fuel has been consumed - Correct - In the life cycle of the star, after all of the hydrogen and helium fuel has been burned, the delicate balance between the outer nuclear radiation.pressure and the stable gravitational force becomes disturbed and slow contraction begins.

4. The author asserts that the discoveries of the white dwarf, the neutron star, and the black hole are significant because these discoveries.

A. demonstrate the probability of infinite density and infinitely small dimensions - Incorrect - we have this only in the case of black holes
B. pose the most comprehensive and fundamental problem faced by physicists in decades - Correct
C. clarify the paradox suggested by the collapse of electrons into atomic nuclei. - Incorrect - this is used an analogy and the discoveries of the white dwarf, the neutron star, and the black hole DO NOT clarify the classical mechanics' paradox
D. establish the relationship between the mass and gravitational pressure. - incorrect
E. assist in establishing the age of the universe by tracing the life histories of stars. - Out of scope

5. The passage contains information that answers which of the following questions? 
I. What is the density limit of the gravitational collapse of neutron stars? -->Gravitational attraction compresses this neutron gas rapidly until a density of 10 tons per cubic inch is reached; at this point the strong nuclear force resists further contraction. 
II. At what point in its life cycle does a star begin to contract? --> In the life cycle of the star, after all of the hydrogen and helium fuel has been burned, the delicate balance between the outer nuclear radiation.pressure and the stable gravitational force becomes disturbed and slow contraction begins.
III . What resists the gravitational collapse of a star? --> 
Gravitational attraction compresses this neutron gas rapidly until a density of 10 tons per cubic inch is reached; at this point the strong nuclear force resists further contraction.

But if the original star was more massive than a few solar masses, even the strong nuclear forces cannot resist the gravitational crunch.

E. I, II, and III - Correct

6. The author introduces the discussion of the paradox concerning atomic structures(in highlighted text) in order to

A. Show why it was necessary to develop quantum mechanics - Irrelevant
B. Compare the structure of an atom with the structure of star - Irrelevant
C. Demonstrate by analogy that a vital insight in astrophysics is missing - Correct -- With the help of quantum mechanics, we could give an explanation for the paradox faced with classical mechanics' explanation of atomic structure. So, we need a similar explanation to account for improbable things such as infinite density and infinitely small dimensions
D. Illustrate the contention that improbable things do happen in astrophysics - Irrelevant
E. Argue that atoms can collapse if their electrons do not remain in orbit. - Incorrect

Answer C

mallya12 · Answer

GMATNinja , workout , GMATNinjaTwo , u1983 , SajjadAhmad , Gnpth The author asserts that the discoveries of the white dwarf, the neutron star, and the black hole are significant because these discoveries. A. demonstrate the probability of infinite density and infinitely small dimensions B. pose the most comprehensive and fundamental problem faced by physicists in decades C. clarify the paradox suggested by the collapse of electrons into atomic nuclei. D. establish the relationship between the mass and gravitational pressure. E. assist in establishing the age of the universe by tracing the life histories of stars. I am a little confused here. Isn't the discovery of infinite density and infinitely small dimensions calling into the question the existing theories. Then how do the discoveries pose "problem faced by physicists in decades " . It was only after the discovery the scientist faced problems. Please explain. Thank You

GMATNinja · Answer

The most relevant piece of the passage to answer question #4 is the very first sentence:
 
Here, the author asserts that the significance of these discoveries is that they present physicists with a great challenge -- the greatest since the failure of classical mechanics. Because they are "among the most exciting developments  in decades ," we can further extrapolate that the failure of classical mechanics happened decades before the discovery of these stars.

Take another look at (B):
 
You are correct that the scientists only faced the "problem" of these kinds of stars  after  they discovered the stars. However, this is exactly why the author believes these discoveries to be significant -- before the discovery of the stars, physicists spent decades lounging about (or working on smaller issues, I guess) without any major problems to solve. Once they discovered these types of stars, they finally had a big challenge to work on. (B) is the correct answer.

Now take a look at (A):
 
The question stem asks about the significance of discovering "the white dwarf, the neutron star, and the black hole." Only black holes achieve "infinite density and infinitely small dimensions." Because (A) does not address two out of three of the phenomena in question, it is not a good answer for this question. Also, the discovery of black holes does not necessarily "demonstrate the  probability of infinite density and infinitely small dimensions" -- it just provides evidence to support the "most widely accepted theories" that predicted the existence of infinite density/infinitely small dimensions. The author never asserts that black holes demonstrate the probability of this occurrence, so (A) is out.

I hope that helps!

Manat · Answer

GMATNinja   workout

In Question 7, how do you eliminate A? i understand how D is the correct answer but the following lines support A as well :-

"It may well be that an equivalent advance awaits us in investigating the theoretical problems presented by the phenomenon of gravitational collapse

tkorzhan1995 · Answer

GMATNinja , can you please explain on the basis of what B should be eliminated for Q1?

GMATNinja · Answer

Question 1 
 
Let's start by determining the author's purpose in each paragraph. To do this, we need to figure WHY the author wrote each paragraph. Keep in mind -- we're not just trying to summarize  what  the author said. Rather, we want to understand  why  s/he said it.

Paragraph 1: The author's purpose is to argue that white dwarfs, neutron stars, and black holes may present scientists with "their greatest  challenge  since the failure of classical mechanics." To develop this idea, the author explains how white dwarfs and neutron stars are made.  Paragraph 2: The purpose is to support the argument made in paragraph 1 by describing how black holes are formed.  Paragraph 3: The purpose is to explain why the currently accepted theories about black holes present a challenge to scientists, further supporting the argument made in paragraph 1.

Let's now consider answer choice (B):

The passage certainly does explain the origins of black holes, neutron stars, and white dwarfs. But is that the primary purpose -- to simply  explain  how those things are made? Is that WHY the author talks about those types of stars?

Going back to our analysis of the author's purpose in each paragraph, we see the author doesn't describe the origins of black holes and other stars as an end in itself. Rather, they're described in order to support a larger argument -- more specifically, that scientists are facing a huge  challenge .

So while the author does explain the origin of black holes, neutron stars, and white dwarfs, this isn't the primary purpose of the passage. Eliminate (B).

Let's consider (D):

According to our analysis, the reason the author mentions black holes and other stars is to support the idea that physicists are facing a major challenge. Since answer choice (D) captures this larger purpose, it's correct.

I hope that helps!

VerbalBot · Answer

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The discoveries of the white dwarf, the neutron star, and the black

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