Image: WOLFGANG BRANDNER, EVA K. GREBEL (Universitat Wurzburg), et al., and the European Southern Observatory SUPERNOVA EXPLOSION. Sher 25 (arrow) is a massive blue star, surrounded by an hourglass nebula it ejected 6,600 years ago. Most probably, it will explode as a supernova, paving the way for the formation of a black hole.

By the time this matter has fallen past the point of no return, called the event horizon, it has concentrated the angular momentum of the black hole into a very small volume, which greatly distorts the surrounding space-time. The angular momentum persists even after the matter that caused it has cut itself off from our universe, collapsing beyond the event horizon.

Presently, a team of researchers at Stanford University is designing the Gravity Probe satellite to measure the distortion of space-time due to the angular momentum of our own spinning Earth. Although the space-time distortion near Earth is exceedingly weak compared to that around a black hole, the same physics are at work. Measuring this distortion would offer further support for Einstein's Theory of General Relativity.

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