Blackholes are actually 'green'
 

Blackholes are regions of space where gravity is so strong that matter and light can't escape once they pass the event horizon, a spherical boundary surrounding the blackhole.

However inflowing matter that hasn't yet passed this point of no return can, through friction and interaction with the black hole's strong magnetic field, release energy in the form of either diffuse light or focused jets of energy.

"Once gas comes within a distance about a million times larger than the event horizon of the black hole, it becomes gravitationally captured," Allen explained. "At this point the gas becomes fuel for the black hole engine."

The new study looked at nine supermassive blackholes at the centers of elliptical galaxies; each about a billion times bigger than the sun. The blackholes were relatively old and generated much less energy than the fiercely luminous and rapidly growing supermassive black holes known as "quasars."

Researchers found that these "quiet" blackholes released about 1,000 times more energy as jets than as light. The reasons for this are still unclear.

"That's a mystery, how these black holes selectively put that much energy into the jets without producing much light," study team member Christopher Reynolds from the University of Maryland told SPACE.com.