By Ron Cowen
For all their mind-boggling effects on geometry, warping the very fabric of space and time, black holes are governed by two just properties–mass and spin.
Although these superdense objects don’t emit light, their mass can be measured with relative ease if they are partnered with a visible star. Astronomers simply record how much of a tug a black hole exerts on its companion. Determining whether a black hole rotates has proven much more of a challenge. Astronomers reported last week strong evidence that black holes spin like whirling dervishes, dragging space-time along with them.