Logical Reasoning

PT137 · S3 · Q10 A ring of gas emitting X-rays

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A ring of gas emitting X-rays flickering 450 times per second has been observed in a stable orbit around a black hole.

Premise

A ring of gas flickering 450 times per second has been observed in stable orbit around a black hole.

Premise

That flickering rate is best explained, given accepted physics, if the ring has a 49-km radius.

Premise

A gas ring couldn't maintain such a close orbit (49-km radius) unless the black hole was spinning.

Anticipate

Chain: observed 450/sec flickering -> ring has 49-km radius -> black hole must be spinning. So the most supported claim is that this particular black hole is spinning.

Goal

Find the answer that says this black hole is spinning.

10.

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

  1. Black holes that have orbiting

    Unsupported

    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.

    5% picked this

  2. Only rings of gas that

    Too Strong

    "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% picked this

  3. Correct

    The black hole that is

    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.

    82% picked this

  4. X-rays emitted by rings of

    Unsupported

    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% picked this

  5. A black hole is stationary

    Unsupported

    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% picked this

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