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A black hole is a region of spacetime from which gravity prevents anyt

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A black hole is a region of spacetime from which gravity prevents anyt [#permalink]

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New post 15 Oct 2016, 12:05
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A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of a stellar mass (the mass of our sun) or greater.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is a general consensus that supermassive black holes exist in the centers of most galaxies.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a large black hole, their orbit can be used to determine its mass and location. These data can be used to exclude possible alternatives (such as neutron stars). In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the core of our Milky Way galaxy contains a supermassive black hole of about 4.3 million solar masses.

[Reveal] Spoiler:
D

1. Which of the following can be inferred from the passage about larger black holes?

(A) They are more likely to be found in the center of galaxies than elsewhere in the universe
(B) They are typically formed when neutron stars collapse
(C) They emit radiation at a higher temperature than do smaller black holes
(D) They affect the orbit of nearby stars
(E) They form accretion disks more frequently than do smaller black holes


[Reveal] Spoiler:
C

2. According to the passage, all of the following would be helpful in discovering new supermassive black holes in the universe except

(A) Observing interactions with matter
(B) Observing interactions with electromagnetic radiation
(C) Observing levels of emitted radiation
(D) Analyzing the orbits of stars
(E) Focusing on the centers of major galaxies


[Reveal] Spoiler:
D

3. The primary purpose of the passage above is to

(A) Analyze a surprising scientific discovery
(B) Argue that black holes are important to the scientific community
(C) Explain how supermassive black holes are formed
(D) Describe a scientific phenomenon
(E) Compare two types of black holes


[Reveal] Spoiler:
D

4. The author points out that a black hole can continue to grow by absorbing mass in order to:

(A) explain how black holes of stellar mass initially form.
(B) explain why supermassive black holes exist in the centers of most galaxies.
(C) provide evidence for why there is a general consensus that supermassive black holes exist.
(D) account for the existence of supermassive black holes.
(E) support the notion that supermassive black holes form only when very massive stars collapse.

[Reveal] Spoiler: Question #1 OA
[Reveal] Spoiler: Question #2 OA
[Reveal] Spoiler: Question #3 OA
[Reveal] Spoiler: Question #4 OA

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Re: A black hole is a region of spacetime from which gravity prevents anyt [#permalink]

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New post 17 Oct 2016, 06:08
Top Contributor
1.
A - All we know from the passage is this - "There is a general consensus that supermassive black holes exist in the centers of most galaxies.". Supermassive blackholes are a subset of larger blackholes. So we cannot infer anything like this about larger blackholes from supermassive blackholes.
B - No such thing is mentioned in the passage. The passage only states that they are formed from very massive stars.
C - We know that this is not true. Radiation temperature is inversely proportional to their mass. Hence, larger black holes emit radiation at lower temperature. Also, note that the argument states that event horizons emit radiation not the black holes themselves. Eliminate C.
D - Correct answer - " If there are other stars orbiting a large black hole, their orbit can be used to determine its mass and location."
E - All we know is this - "Matter falling onto a black hole can form an accretion disk heated by friction". We cannot infer option E from this sentence.

2.
look at these sentences -
" inferred through its interaction with other matter and with electromagnetic radiation such as light. "
"If there are other stars orbiting a large black hole, their orbit can be used to determine its mass and location."
"There is a general consensus that supermassive black holes exist in the centers of most galaxies."
Only C remains.

3.
A - nowhere is the passage talking about a "discovery" and nowhere does it mention it to be "surprising". It just describes blackholes.
B - nowhere is the importance of blackholes mentioned.
C - this is mentioned only in the 2nd sentence of the 2nd paragraph. Not the main idea.
D - Correct answer. the passage describes blackholes.
E - what two types? and nowhere is there any comparison mentioned.
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Re: A black hole is a region of spacetime from which gravity prevents anyt [#permalink]

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New post 17 Oct 2016, 06:16
casperatwork wrote:
A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of a stellar mass (the mass of our sun) or greater.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is a general consensus that supermassive black holes exist in the centers of most galaxies.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a large black hole, their orbit can be used to determine its mass and location. These data can be used to exclude possible alternatives (such as neutron stars). In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the core of our Milky Way galaxy contains a supermassive black hole of about 4.3 million solar masses.


1. Which of the following can be inferred from the passage about larger black holes?

A.They are more likely to be found in the center of galaxies than elsewhere in the universe
B.They are typically formed when neutron stars collapse
C.They emit radiation at a higher temperature than do smaller black holes
D.They affect the orbit of nearby stars
E.They form accretion disks more frequently than do smaller black holes

2.According to the passage, all of the following would be helpful in discovering new supermassive black holes in the universe except _______________________

A.Observing interactions with matter
B.Observing interactions with electromagnetic radiation
C.Observing levels of emitted radiation
D.Analyzing the orbits of stars
E.Focusing on the centers of major galaxies

3.The primary purpose of the passage above is to _______________________

A.Analyze a surprising scientific discovery
B.Argue that black holes are important to the scientific community
C.Explain how supermassive black holes are formed
D.Describe a scientific phenomenon
E.Compare two types of black holes



Got ACD-will be interested to know how D is the answer too the first question. It is nowhere given the blackholes affect the orbit whereas option A is given.

Thanks.

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A black hole is a region of spacetime from which gravity prevents anyt [#permalink]

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New post 28 Nov 2017, 05:55
casperatwork wrote:
A black hole is a region of spacetime from which gravity prevents anything, including light, from escaping. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that marks the point of no return. The hole is called "black" because it absorbs all the light that hits the horizon, reflecting nothing, just like a perfect black body in thermodynamics. Quantum field theory in curved spacetime predicts that event horizons emit radiation like a black body with a finite temperature. This temperature is inversely proportional to the mass of the black hole, making it difficult to observe this radiation for black holes of a stellar mass (the mass of our sun) or greater.

Black holes of stellar mass are expected to form when very massive stars collapse at the end of their life cycle. After a black hole has formed it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses may form. There is a general consensus that supermassive black holes exist in the centers of most galaxies.

Despite its invisible interior, the presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as light. Matter falling onto a black hole can form an accretion disk heated by friction, forming some of the brightest objects in the universe. If there are other stars orbiting a large black hole, their orbit can be used to determine its mass and location. These data can be used to exclude possible alternatives (such as neutron stars). In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the core of our Milky Way galaxy contains a supermassive black hole of about 4.3 million solar masses.
4. The author points out that a black hole can continue to grow by absorbing mass in order to:

(A) explain how black holes of stellar mass initially form.
(B) explain why supermassive black holes exist in the centers of most galaxies.
(C) provide evidence for why there is a general consensus that supermassive black holes exist.
(D) account for the existence of supermassive black holes.
(E) support the notion that supermassive black holes form only when very massive stars collapse.



Solution



For this function style question, you should first locate where the information given in the question stem is discussed and then examine the context around it. The author talks about a black hole continuing to grow by absorbing mass in the 2nd and 3rd sentence of the 2nd paragraph. Looking at the context, you see that the first sentence simply describes how black holes of stellar mass initially form. Then the author uses the fact that these black holes can absorb mass around them to turn into supermassive black holes.

As a result, answer choice (D) is correct – the author uses this fact to account for how black holes of stellar mass can then become supermassive.

For (A), the fact they absorb mass around them has nothing to do with how they initially form – this is a secondary process after a massive star collapses.

For (B), this fact does not explain at all why they are at the centers of most galaxies – it simply explains how they can go from one stellar mass to millions of stellar masses.

Like (B), the general consensus relates to the fact that they are often found at the center of galaxies, and the author does not use this fact to explain why that is true.

(E), like (A), is incorrect because this fact does help explain anything relating to the initial formation of the black hole.

Correct answer is (D).
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A black hole is a region of spacetime from which gravity prevents anyt   [#permalink] 28 Nov 2017, 05:55
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