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Explanation: How fast can a black hole spin? If any object made of regular matter spins too fast -- it breaks apart. But a black hole might not be able to break apart -- and its maximum spin rate is really unknown. Theorists usually model rapidly rotating black holes with the Kerr solution to Einstein's General Theory of Relativity, which predicts several amazing and unusual things. Perhaps its most easily testable prediction, though, is that matter entering a maximally rotating black hole should be last seen orbiting at near the speed of light, as seen from far away. This prediction...

Embedded in the heart of a supernova remnant 10,000 light-years away is a stellar object the likes of which astronomers have never seen before in our galaxy. At first glance, the object looks like a densely packed stellar corpse known as a neutron star surrounded by a bubble of ejected stellar material, exactly what would be expected in the wake of a supernova explosion. However, a closer 24.5-hour examination with the European Space Agency's XMM Newton X-ray satellite reveals that the energetic X-ray emissions of the blue, point-like object cycles every 6.7 hours-tens of thousands of times longer than expected...

Using data from ESA's XMM-Newton X-ray observatory, an international group of astrophysicists has discovered a spinning neutron star that seems to be tumbling slowly - a find that could provide new insight into the evolution and structure of these super-dense objects. Spinning neutron stars, also known as pulsars, generally rotate on highly stable axes. Thanks to their periodic signals, emitted either in radio or X-ray wavelengths, they can serve as very accurate astronomical clocks. Regarding pulsar RX J0720.4-3125, however, the team found that over the past four and a half years, its temperature has been rising - until very recently,...