LSAT Explanation PT 29, S4, Q23: Quasars—celestial objects so far away that

LSAT Question Stem

If the statements above are true, which one of the following must also be true on the basis of them? 

Logical Reasoning Question Type

This is a Must Be True question. 

Correct Answer

The correct answer to this question is E. 

LSAT Question Complete Explanation

Let's break down the passage first to understand the information provided about quasars:

1. Quasars are celestial objects so far away that their light takes at least 500 million years to reach Earth.

2. To appear from Earth the way quasars do, they would have to burn steadily at a rate that produces more light than 90 billion suns.

3. Nothing that burns at a rate that produces that much light could exist for more than about 100 million years.

Now, let's analyze the question type and what it's asking us to do. This is a Must Be True (MBT) question, which means we need to find the answer choice that must be true based on the information provided in the passage.

Let's go through each answer choice and evaluate them based on the passage:

a) Instruments in use before 1963 were not sensitive enough to permit quasars to be seen.

- The passage does mention that quasars have been seen since 1963, but it does not provide any information about the instruments used before 1963. So, we cannot conclude that this must be true.

b) Light from quasars first began reaching Earth in 1963.

- The passage states that quasars have been seen since 1963, but it does not imply that the light from quasars first began reaching Earth in 1963. This answer choice is not supported by the passage.

c) Anything that from Earth appears as bright as a quasar does must produce more light than would be produced by 90 billion suns.

- The passage only talks about quasars and the light they produce. It does not make a general statement about "anything" that appears as bright as a quasar. So, this answer choice is too broad and not supported by the passage.

d) Nothing that is as far from Earth as quasars are can continue to exist for more than about 100 million years.

- This answer choice is also too broad. The passage only states that nothing that burns at a rate that produces that much light could exist for more than about 100 million years. It does not make a general statement about the existence of all objects as far from Earth as quasars.

e) No quasar that has ever been seen from Earth exists any longer.

- This answer choice is supported by the passage. Since quasars are so far away that their light takes at least 500 million years to reach Earth and nothing that burns at a rate that produces that much light could exist for more than about 100 million years, by the time we see the light from a quasar on Earth, it would have already ceased to exist for at least 400 million years. So, this answer choice must be true based on the passage.

Therefore, the correct answer is E.