A New Method To Measure Black Hole's Spin
Black holes are defined by only three parameters: mass, charge and spin. We know that black holes spin. But how can we measure that? What tools and methods are at our disposal? Answering these questions with Dr Ruth Daly, Professor of Physics at Penn State University.
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Comments (4)
Let’s try this, Fraser. I fire my 4B at the 6B M87 so that it just passes by the 6B’s event horizon in both the 6B’s and 4B’s spin direction. The 6B, being the Big Dog, will do what? Gain rest mass? Gain rotational mass? Surely not much spin since it is already at 1? A combination of the three?
Fraser, assuming M87 is 6B solar masses and has a spin of EXACTLY 1, what would happen if a supermassive black hole with, oh, 4B solar masses were to impact it in the spin direction. On the one hand, I would guess the spin rate would increase since we’re now dealing with roughly 10B solar masses instead of 6B, but I kinda got the impression that spin doesn’t behave exactly … linearly. If we can’t bust the 1.0 barrier, what happens to the extra spin?
Sgr A* (with a radius of 10 × Sun's radius) can't spin every 2 minutes (it would exceed c) so it must be for comparison with M87 spinning every 2 days.
Do we assume that a black hole system is a closed or open system?