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Rocket your D&D 5E and Level Up: Advanced 5E games into space! Alpha Star Magazine Is Launching... Right Now!

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Message: <blockquote data-quote="Umbran" data-source="post: 6094053" data-attributes="member: 177">Well, here's a bit of an issue when you say they have "confirmed" the spin on a black hole.  Here I put on my pedantic hat.You can't observe the hole directly.  For a black hole, we expect an, "innermost stable orbit".  Get any closer, and matter can't be in a long-term orbit around the hole - it is either falling in, or escaping.  Hanging around is not an option.  The math says that, if the hole is spinning, it twists space in a particular way, and that leads to an ISO that is rather closer than for a non-spinning hole.  My quick read of secondary sources (I haven't read the Nature article, yet) goes thusly:  They got a good look at the accretion disk around a super-massive black hole*.  Measuring how far that is from the hole, they assume the inner-edge of the disk is at the innermost stable orbit, and thus derive how quickly the hole is spinning. Simple enough.But, "confirmation" generally requires that you have *two* ways to measure something, and they agree.  One measurement, using a theoretical construct as to the measurement's meaning, is not "confirmation" of that meaning.  If we accept the measurement, though, it does have implications for how these holes come to be.  If you expect most of the growth is from random infalling material, then you expect the hole's spin to decrease as it grows - the infalling matter, coming in at random angles, will overall add no angular momentum.  Adding mass but no momentum over time means you're generally slowing the spin.  But, this bugger is spinning *fast* - at about 84% of the maximum allowed by relativity**.  This implies that the hole grew in some sort of ordered way or process - in general, stuff falling in added to its angular momentum, rather than falling in randomly as we'd expect.*Not directly - it was a complicated thing, that includes determining the red-shift of X-rays coming off the heated gas of the disk.**You'll see reports that it is spinning "at 84% of the speed of light".  That's a bit misleading, as there's no hard surface or particle on the hole (that we can see) that is physically moving at all.  </blockquote>

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