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Reuters reports on Black holes turning out to be ‘green’ (as in environmentally-friendly):

Just how efficient? If a car could use this kind of engine, it could theoretically go about a billion miles (1.6 billion km) on a gallon of gas, said Steve Allen of Stanford University in California.

Pretty impressive. Also,

These supermassive black holes are “green” in another way, said Kim Weaver of NASA’s Goddard Space Flight Center: they appear to limit star formation and galactic sprawl.

The heat coming from the black hole jets is believed to heat up the gas around the galactic center; without this source of heat, the gas would cool down and form new stars, Weaver said.

“This is one way to keep the stars from forming and letting the galaxies grow bigger,” she said.

Nature, Space, Energy