A ring of gas emitting X-rays

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsMost Supported

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Stimulus

A ring of gas emitting X-rays flickering 450 times per second has been observed in a stable orbit around a black hole. In light of certain widely accepted physical theories, that rate of flickering can best be explained if the ring of gas has a radius of 49 kilometers. But the to a black hole unless the black hole was spinning.

What this question is testing

Most Supported

Premises

The argument hands us a chain of physics. We see a gas ring flickering 450 times per second. Physics says that flickering rate fits best with a 49-km-radius ring. And a ring that close to a black hole can only stay in stable orbit if the black hole is spinning.

Anticipate

Walk it down: flickering at 450/sec -> ring is 49 km out -> black hole is spinning. The conclusion most strongly supported is that this particular black hole is spinning.

Goal

Look for the answer that picks up the bottom of that chain — this black hole is spinning.

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The question

10.

The statements above, if true, most strongly support which one of the following, assuming that the widely accepted physical theories referred

Answer choices

Unsupported6% picked this
Black holes that have orbiting rings of gas with radii greater than 49 kilometers
The stimulus only tells us about gas rings at 49 km — not larger rings. We have no information about black holes with larger orbiting rings, and no support for a generalization that they're "usually stationary." The stimulus only entails what's required for the close orbit, not what happens at greater distances.
6%
Too Strong3% picked this
Only rings of gas that are in stable orbits around black holes
"Only" is too strong. The stimulus says this particular ring (in stable orbit) emits flickering X-rays. It doesn't say only stable-orbit rings can do so. There could be unstable rings that also emit flickering X-rays.
3%
Correct81% picked this
The black hole that is within the ring of gas observed by the
Why this is right
Walk the chain. The observed ring flickers at 450/sec, which fits best with a 49-km radius. A ring at that radius can only maintain its stable orbit if the black hole is spinning. The ring is in stable orbit — therefore the black hole is spinning.
Skill tested: Most Supported · how this choice captures the argument's function is the move to repeat next time.
81%
Unsupported5% picked this
X-rays emitted by rings of gas orbiting black holes cause those black
The stimulus says the spinning is needed to support the orbit, not that the X-rays cause the spinning. This reverses the causal direction the stimulus implies. There's no support for the idea that the X-rays make the black hole spin.
5%
Unsupported5% picked this
A black hole is stationary only if it is orbited by a ring of gas with a radius
The stimulus tells us a 49-km ring requires a spinning black hole, but it doesn't say larger-ring black holes are stationary. A black hole could be spinning whether its gas ring is at 49 km or much larger. This answer's "only if" rule is unsupported.
5%

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