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Black Hole's Spin Revealed for 1st Time
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<blockquote data-quote="freyar" data-source="post: 6094835" data-attributes="member: 40227"><p>Umbran's right (and in ahead of me, as usual), but I'll add a bit more below.</p><p></p><p></p><p></p><p>Well, the hope (of most people anyway) is that the ultimate theory of gravity will smooth out the "singularity" into something nonsingular. The presence of a singularity is really telling us that we shouldn't trust GR near that location. But, you're right, there's no consensus about what the correct theory is (there are a number of good candidates, depending on how you count them).</p><p></p><p></p><p></p><p>That's true, but that's a quantum mechanical property of the electron. These black holes are classical objects, so you'd think it would need</p><p>size to carry angular momentum.</p><p></p><p>The catch is that it's not actually the singularity that carries the angular momentum, at least not in the GR way of looking at things. One issue is that, once you're working in gravity, defining angular momentum (or even energy) is a bit more subtle than what we're used to. The upshot, though, is that one way (maybe the best one) to think about things is that the spacetime itself <em>outside the horizon</em> carries the angular momentum. In fact, if you really get down to it, you can figure out the energy or angular momentum only by looking at spacetime an infinite distance away from the black hole. Anyway, one of the points is that measurements are a bit tricky in gravitational situations.</p><p></p><p>I found some papers a few weeks ago that showed tables of spin measurements, so this doesn't seem to be the absolute first measurement.</p><p></p><p>Thx!</p><p></p><p>TomB</p></blockquote><p>[/QUOTE]</p>
[QUOTE="freyar, post: 6094835, member: 40227"] Umbran's right (and in ahead of me, as usual), but I'll add a bit more below. Well, the hope (of most people anyway) is that the ultimate theory of gravity will smooth out the "singularity" into something nonsingular. The presence of a singularity is really telling us that we shouldn't trust GR near that location. But, you're right, there's no consensus about what the correct theory is (there are a number of good candidates, depending on how you count them). That's true, but that's a quantum mechanical property of the electron. These black holes are classical objects, so you'd think it would need size to carry angular momentum. The catch is that it's not actually the singularity that carries the angular momentum, at least not in the GR way of looking at things. One issue is that, once you're working in gravity, defining angular momentum (or even energy) is a bit more subtle than what we're used to. The upshot, though, is that one way (maybe the best one) to think about things is that the spacetime itself [I]outside the horizon[/I] carries the angular momentum. In fact, if you really get down to it, you can figure out the energy or angular momentum only by looking at spacetime an infinite distance away from the black hole. Anyway, one of the points is that measurements are a bit tricky in gravitational situations. I found some papers a few weeks ago that showed tables of spin measurements, so this doesn't seem to be the absolute first measurement. Thx! TomB[/QUOTE] [/QUOTE]
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