Scientists studying the energy output of black holes have discovered to their surprise that "the conversion of energy by matter falling toward a black hole is much more efficient than nuclear or fossil fuels" - so much so that "if a car was as fuel-efficient as these black holes, it could theoretically travel more than a billion miles on a gallon of gas".

That's according to boffins at the Chandra X-Ray Observatory, who studied the inner regions of nine elliptical galaxies with a view to determining the rate at which gas is being sucked towards said galaxies' supermassive black holes.

As the gas falls towards the event horizon, it releases energy in the form of high-energy particles which stream away in jets from a "magnetised gaseous disk" encompassing the black hole's core (see pic). These jets then form enormous "bubbles" far out into space.

The question for the Chandra team was how much energy would be required for the jets to produce these bubbles, in some cases thousands of light years across? The answer, according to Steve Allen of Stanford University, is a trillion trillion trillion watts.

The upshot of this fuel-efficient conversion rate, Reuters notes, is that big black holes theoretically have enough gas to keep firing for hundreds of billions of years, way beyond the current estimated age of the universe - a modest 13.7bn years.

A knock-on effect of the black holes' emissions, says Kim Weaver of NASA's Goddard Space Flight Centre, is that the outpouring of energy heats up the gas surrounding the galactic centre, thereby preventing stars from forming from cooling gaseous matter.

Weaver said: "This is one way to keep the stars from forming and letting the galaxies grow bigger." ®