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

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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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1. The primary purpose of the passage is to

D. explain how the collapse of stars challenges accepted theories of physics.
It may well be that an equivalent t advance awaits us in investigating the theoretical problems presented by the phenomenon of gravitational collapse.

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

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.

The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the red giant are among eh most exciting developments in decades because they may be well present physicists with their greatest challenge since thefailure 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...., 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

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

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

B
The discoveries of the white dwarf, the neutron star, and the black hole, coming well after the discovery of the red giant are among eh most exciting developments in decades because they may be well present physicists with their greatest challenge since thefailure of classical mechanics.

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

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

C. Demonstrate by analogy that a vital insight in astrophysics is missing

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

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.

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.
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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P1 - discovery of red giant, How neutron star forms
P2 - How a star become black hole.

1. The primary purpose of the passage is to

D. explain how the collapse of stars challenges accepted theories of physics. --- this one is best covering the whole passage.

------------------------------------
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 --- our own sun is small that is why only According

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

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

C. radiation pressure decreases when a star’s fuel has been consumed

------------------------------------------

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

because they may be well present physicists with their greatest challenge since the failure of classical mechanics

B. pose the most comprehensive and fundamental problem faced by physicists in decades

-------------------------------------

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

Straight E. No doubt all can be answered.

--------------------------------------------------------

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 - no, this was not the aim.
B. Compare the structure of an atom with the structure of star - not comparison.
C. Demonstrate by analogy that a vital insight in astrophysics is missing -
D. Illustrate the contention that improbable things do happen in astrophysics - 1.st nothing mentioned as improbable. 2nd atomic structure was not an Illustration.
E. Argue that atoms can collapse if their electrons do not remain in orbit. - no
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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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

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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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It came to my attention that the GMAT somewhat likes discussing astrophysics...

I have noticed, while reading through the passage, that a show, concerning stars and our universe, I watched a couple of weeks ago at my local planetarium actually helped me to understand this rather complex and technical passage! The show used a visual approach to explain the complexity of dying stars, which helped me to understand the processes described in the passage.

Maybe it helps other people too, definitely payed off in this question!
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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.

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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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mallya12 wrote:
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.

The most relevant piece of the passage to answer question #4 is the very first sentence:
Quote:
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 well present physicists with their greatest challenge since the failure of classical mechanics

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):
Quote:
B. pose the most comprehensive and fundamental problem faced by physicists in decades

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):
Quote:
A. demonstrate the probability of infinite density and infinitely small dimensions

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 probabilityof 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!
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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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
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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Took 4:20 min to read and then around 0:50 min per Q.

Passage Map:

1) New Discovery; Format of White Dwarf and Neutron Star
2) Formation of Black Hole
3) Paradox. Analogy to atomic structure.
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
GMATNinja, I selected originally A for Q7 based on the following:
Studies centered around paradox led to the development of quantum mechanics.

Since studies led to the development of quantum mechanics, new discoveries can be made.

Can you please help me to understand where I am getting wrong with my analysis of this question?
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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tkorzhan1995 wrote:
GMATNinja, I selected originally A for Q7 based on the following:
Studies centered around paradox led to the development of quantum mechanics.

Since studies led to the development of quantum mechanics, new discoveries can be made.

Can you please help me to understand where I am getting wrong with my analysis of this question?

Take a look at this post and see whether that clears things up!
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The discoveries of the white dwarf, the neutron star, and the black [#permalink]
Question 7 Option A and D confused me massively as well. After much thought, here's what I understood:

The development of quantum physics or any impending discovery is one result of understanding the paradox. But the paradoxes themselves are useful because they help to point out gaps or inadequacies in the existing theories. This may or may not lead to new discoveries.

Think of it like Paradox--->understanding gaps---> new discoveries (maybe)

So option A is likely, but option D is a definite outcome.
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
GMATNinja, can you please explain on the basis of what B should be eliminated for Q1?
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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Question 1

tkorzhan1995 wrote:
GMATNinja, can you please explain on the basis of what B should be eliminated for Q1?

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):

Quote:
1. The primary purpose of the passage is to

B. explain the origins of black holes, neutron stars, and white dwarfs.

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):

Quote:
D. explain how the collapse of stars challenges accepted theories of physics.

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!
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
Is this a 700 level passage? It seems to be at 650 max. Sajjad1994
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
mayankkkk wrote:
Is this a 700 level passage? It seems to be at 650 max. Sajjad1994

Here is the difficulty level of each question, in my opinion.

Question #1: 600-650
Question #2: 650-700
Question #3: 700
Question #4: 600
Question #5: 700
Question #6: 550-600
Question #7: 700-750
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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Re: The discoveries of the white dwarf, the neutron star, and the black [#permalink]
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