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Stellar objects are dynamic systems involving a symbiotic relationship

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Stellar objects are dynamic systems involving a symbiotic relationship  [#permalink]

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New post Updated on: 12 Oct 2019, 09:24
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New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 385, Date: 12-Oct-2019
This post is a part of New Project RC Butler 2019. Click here for Details


Stellar objects are dynamic systems involving a symbiotic relationship between matter and radiation. Thermonuclear fusion, the thermally-induced combining of nuclei as they tunnel through the Coulomb barrier, is responsible for supporting stars against gravitational contraction and the ultimate fate of a star depends upon its remaining mass once thermonuclear fusion can no longer provide the pressure required to counteract gravity.

In a live star, the hot center allows hydrogen to fuse into helium, but once the core has burned all available hydrogen, it will contract until another source of support becomes available. If the star is massive enough, as the core contracts and heats, transforming gravitational energy into kinetic energy, it begins burning helium ashes and producing iron, the most stable of nuclei. This thermonuclear burning continues until it produces an iron core at the heart of the star. The three final forms a star can hold are a white dwarf, a neutron star, or a black hole.

Our Sun will expand and expel most of its outer matter to create a planetary nebula. The remaining core will cool, and at
some point the Fermi pressure of the degenerate electrons will become sufficient to counteract the gravitational pressure; the sun will stabilize. The result will be a relatively cold compact object: a white dwarf star.

In stark contrast, neutron stars result from one of the most cataclysmic events in the universe, the death of a star with a mass much greater than that of our Sun. Electrons in these stars behave ultra-relativistically and hydrostatic equilibrium becomes impossible to achieve. During the collapse of the core, a supernovae shock develops ejecting most of the mass of the star into interstellar space and leaving behind an extremely dense core: the neutron star.

As a star collapses into a neutron core, it begins to lose mass in the form of neutrino radiation. The loss of mass relieves sustaining pressure provided by the core and if that pressure is reduced to the limit beyond which it can not prevent gravitational contraction, the star will collapse into an object of zero radius: a black hole.


1. According to the passage which of the following is not true of all stars?

(A) They generated helium as a product of thermonuclear fusion.
(B) They rely on internally produced pressures to counteract the effects of gravity on their own mass.
(C) They possess cores hot enough to combine nuclei.
(D) They eventually produce iron cores through thermonuclear burning.
(E) Their ultimate form is related to the mass they possess as they begin to die.



2. The primary purpose of the passage is to

(A) present a commonplace idea and its inaccuracies
(B) explore the implications of a finding
(C) propose a hypothesis for unexplained observations
(D) analyze a frequent source of misunderstanding
(E) describe a process and its outcomes



3. Which of the following can most logically be inferred from the passage?

(A) Our Sun has fused the majority of the hydrogen contained within it.
(B) A supernovae shock precedes the formation of a black hole.
(C) Neutrino radiation is caused by ultra-relativistically electrons.
(D) Fermi pressure is brought about by the gravitational pressure of a collapsing star.
(E) A white dwarf star is incapable of melting the tails of passing comets.



QUESTION-1
The second sentence of paragraph two states that stars produce iron cores only if they have sufficient mass.
Thus, not all stars produce iron cores. Choice D is correct.

QUESTION-2
The passage describes a process that begins "once thermonuclear fusion can no longer provide the pressure required to counteract gravity" in a star. Specifically, the passage describes the three possible outcomes for stars as they "die."
Thus, choice E is the best choice.

QUESTION-3
Paragraph five indicates that when a star collapses into a neutron stars it may continue to collapse further into a black hole. Since paragraph four states that neutron star formation is preceded by a supernovae shock, black hole formation must therefore also be preceded by a supernovae shock. Choice B is correct.

Originally posted by shridhar786 on 10 Oct 2019, 19:49.
Last edited by SajjadAhmad on 12 Oct 2019, 09:24, edited 1 time in total.
Updated - Complete topic (957).
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Re: Stellar objects are dynamic systems involving a symbiotic relationship  [#permalink]

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New post 16 Jan 2020, 21:58
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Hi there. I am not a verbal expert, but I want to practice myself. So I will try to explain my understand. Please help me fix if I am wrong in some points. :lol:

The first question ask about which one is not true of all stars. So from my understand, I have to understand the overall structure so that I can find the location where there are details that tell me about info of every stars, not just one type of stars. The structure of each paragraph will be like
- Para 1&2: common characters of all stars
- Para 3: white dwarf
- Para 4: the neutron star
- Para 5: black hole

How I know it?
- The last sentence of 2nd paragraph is "The three final forms a star can hold are a white dwarf, a neutron star, or a black hole." So I can think that OK after this they may tell about these 3 final form
- And yes they tell about it in each paragraph! We can easily spot from the last word of each para 3&4&5

So now I know that I have to look into para 1&2 in order to get answer since these paragraphs talk about overall stars details.

For me this question is hard, but OK, let's look at the choices
1. According to the passage which of the following is not true of all stars?
(A) They generated helium as a product of thermonuclear fusion.
So it basically says that Thermo -> Helium. In para 2, it says "In a live star, the hot center allows hydrogen to fuse into helium," so it means that the star makes helium. I'm not sure about thermo thing, so it is not 100% right but not wrong either. So I keep it but partly eliminate.
(B) They rely on internally produced pressures to counteract the effects of gravity on their own mass.
So it says that pressure something counteract the gravity. In para 1, it talks about thermo that support stars against gravity, and pressure counteract gravity. So for me I eliminate this choice since it is mentioned. Eliminate.
(C) They possess cores hot enough to combine nuclei.
it does say about "Thermonuclear fusion, the thermally-induced combining of nuclei " which has combine nuclei? So I am not sure but think that this not gonna be a right answer. :lol:
(D) They eventually produce iron cores through thermonuclear burning.
So my understand is that it says that the stars produce ironcore through thermo, which mean that both ironcore and thermo have the action in the same moment. At first I see that, OK, it talks about iron cores. But when I look closely, it says "This thermonuclear burning continues until it produces an iron core at the heart of the star. ". This means that thermo thing continues until it the ironcore is produced, which means that it is not happened at the same time. For me, this choice is very convincing.
(E) Their ultimate form is related to the mass they possess as they begin to die
OK. This choice is stated very clear in the sentence "the ultimate fate of a star depends upon its remaining mass". Eliminate.

So now I got A,C, and D left. But in A,C though i cant find the right explanation, I think that with my current resource, I could eliminate the choices. But in D, it is obvious that the info is not correct. So D is the right answer.


On the second question, this one looks a lot more easy to me.
2. The primary purpose of the passage is to
(A) present a commonplace idea and its inaccuracies; ok it does present idea. But does it mention about inaccuracy? NO. so Eliminate.
(B) explore the implications of a finding; Firstly, it doesnt say that this is a "finding". And it is not "implication", just more of normal information. Eliminate.
(C) propose a hypothesis for unexplained observations; No hypothesis at all. And no mention about unexplain. Eliminate.
(D) analyze a frequent source of misunderstanding; Didn't see any words talk about "misunderstanding" or "frequent source" Eliminate.
(E) describe a process and its outcomes; It says about process of many things (when it says that something is like this, then it will...,then it begins...,then it continues... For me these are clues of "process"). And the "outcomes" are obvious. It talks about 3 outcomes and do describe each in para 3&4&5. So YES we choose this.

PS. in the first question is kind of tough for me. Any experts please give suggestions.
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Re: Stellar objects are dynamic systems involving a symbiotic relationship   [#permalink] 16 Jan 2020, 21:58

Stellar objects are dynamic systems involving a symbiotic relationship

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