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The mass of the galactic center black hole, Srg A*, has been measured to be about 3.5×106 solar masses, far beyond the ~100 solar mass limit for a star. It is also clearly an AGN, though lately inactive. On both these counts it seems to be excluded from the stellar black hole category, although it and all AGN likely were originally born as stellar-mass BHs that later grew by accretion and coalescence. Wwheaton (talk) 20:31, 17 October 2008 (UTC)
Please correct me if I'm wrong, but how can a black hole have a finite rotation frequency? I always understood that all the mass is in a singularity (infinitely small), which will therefore rotate infinitely fast (and thus have a finite angular momentum, which is conserved). Rotation can in my understanding only be measured at a distance, but at the event horizon there is nothing that really moves, it's only the gravity field directed towards the center of the black hole. Can anyone explain this? EmilTyf (talk) 00:11, 30 April 2009 (UTC)
Good question! It would probably have to be something like the period of the last stable orbit (which depends on the hole's angular momentum), but I am just guessing. Let's watch for an expert opinion. Wwheaton (talk) 22:16, 30 April 2009 (UTC)