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

MichelleRod on February 20, 2019

Thanks for your question @Shiyi-Zhang.

The trick to this question is to take what is proposed by "widely-accepted physical theories" as true since the question stem tells us to assume that the theories are correct.

The stimulus begins by offering an observation: a ring of gas emitting light at 450 times per second

Next, an explanation for the observation is proposed: a radius of 49 Kilometers. If we accept the widely held physical theories like the question stem tells us to, then we can take this explanation to be true.

Finally, we are told that a radius as close as the one proposed by the accepted theories would require the black hole to be spinning.

Let's diagram this.

P: 450
P: 450 -> 49
P: 49 -> spinning
- - - - -
C: 450 -> spinning