HEAPOW: Power Going Backward (2010 Jun 14)
Black holes are often thought of as Universal vacuum cleaners, swallowing everything in their path. They're not. But somehow these same black holes can (and do) often generate enormous outflows, "jets", which move outward at incredible speeds (approaching the speed of light). Such jets produced by supermassive black holes at the centers of galaxies are extremely narrow even though they can stretch millions of lightyears. How black holes produce these enormous, extremely thin jets is still a mystery. Astronomers believe these jets are produced by the interplay between a strong magnetic field near the black hole, the rotation of the black hole itself, and a spinning accretion disk of hot plasma feeding the black hole. The exact details still remain to be worked out. New theoretical studies suggest that the black hole spin has an unusual effect on the strength of the jet. This new theory shows that the strongest jets occur in systems in which the black hole rotates in the opposite way to its accretion disk. And that when the black hole and accretion disk rotate in the same way, the jet power is reduced. An implication of this is that in the early Universe, "backward" rotating black holes at the centers of galaxies produced very strong jets; but as time progressed, the black holes and the disks started to rotate in the same way, reducing the jet power.
Backwards Black Holes Might Make Bigger Jets
http://asterisk.apod.com/vie ... 31&t=18304
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