How Black Holes Spit Out Energy express
A whirlpool gulps down water, but splashes most of it back out. That's roughly how a black hole behaves when too much matter falls onto it. In a new study, astrophysicists ran 32 computer simulations to understand how a black hole's parameters — mass, spin, and "appetite"—control these cosmic fountains.
It turns out that the black hole's mass (ranging from 5 to 30 solar masses, where one solar mass is the mass of the Sun) barely matters. The main conductors are the hole's spin and the rate of matter inflow. The black hole swallows only a small fraction of what comes its way: between 10 and 40 percent. The rest is flung away by powerful winds and narrow jets — streams of particles moving at near-light speed. The faster the spin, the more efficient this "engine" becomes: the energy of the wind and jet grows faster than the increase in the infalling matter flow.
The scientists derived formulas linking luminosity, jet power, and the fraction of matter swallowed to the black hole's parameters. These relationships will help astronomers better interpret observations of ultraluminous X-ray sources and other systems where black holes operate at their limits. In this way, we are gradually learning to read the story of each such whirlpool — by how much matter it returns to space.
A black hole with the mass of a star but spinning rapidly can emit more energy into space than the Sun would produce over its entire lifetime.
In Charles Stross's novel Accelerando, an alien probe uses a micro-black hole as an energy source, extracting power from its accretion disk — much like what is described in this work.