"They power engines with incredibly high fuel efficiencies," team leader Steven Allen of Stanford University told reporters via a telephone briefing.

It seems the supermassive black holes - which happen to populate the biggest galaxies in the universe - can produce matter-energy conversion levels of 2.5 percent - or 25 times better than the best nuclear powerplants on Earth. If humans could design a vehicle engine with equivalent efficiency, it could travel a billion miles on a gallon of gasoline.

Allen's team, comprising colleagues from several universities, studied data from NASA's Chandra X-ray Observatory on nine supermassives in the general galactic neighborhood. They found that most of the energy from the objects is released in the form of high-energy jets traveling outward at nearly the speed of light.

The jets - created from the huge infall of gas captured by the black holes' gravity, collide with surrounding clouds of gas in the galaxy that otherwise would have gradually cooled and coalesced into new stars - but the heat of the collisions prevents that process.

"We see enough energy coming out of these black holes to completely stifle star formation," said study co-author Christopher Reynolds of the University of Maryland. "This is an exciting finding because it demonstrates a direct interaction between black holes and galaxy formation, which is a hot topic in astrophysics right now."

The star-forming suppression could be permanent, Reynolds told reporters, because there is enough fuel in these large galaxies to power the process for hundreds of billions of years - or many times the age of the universe.

The team specifically studied relatively old supermassive black holes because they generate much less radiation and therefore have drawn much less scientific attention than quasars - the rapidly growing, brilliantly glowing areas around supermassive black holes that act as beacons of the early universe.

Reynolds and Allen said they became interested in the older supermassives independently, but for the same reason. "They attracted our attention because they were too boring," Reynolds said, explaining that when material is pulled into a black hole, it is converted into radiant energy - but these particular black holes were not generating as much radiation as expected from the amount of material, or fuel falling toward them.

"There had to be something else happening that would explain this discrepancy," he said. Reynolds said he decided to study this type of black hole using data from Chandra that already existed in the public domain. In discussing the idea with colleagues, he discovered that Allen had just begun such a study. "Rather than trying to compete, I decided join up," he said.

Together, Allen, Reynolds and colleagues selected the Chandra data on the nine target supermassives because they were located in relatively nearby galaxies, and therefore they could be studied in greater detail.

The team discovered the black holes were quite active and operating very energy-efficiently - except their so-called missing energy was being produced in the form of particle jets that blasted huge cavities in the surround interstellar gas clouds - and hardly at all in invisible light and only faintly in X-rays.

The researchers calculated the high efficiency of the black hole energy production via particle jets in two steps: First, they used Chandra X-ray images of the inner regions of the galaxies to estimate the amount of fuel available for the black hole. Second, based on the images, they estimated the power required to produce the cavities.

"Just as with cars, it's critical to know the fuel efficiency of black holes," said lead study author Allen of Stanford University. "Without this information, we cannot figure out what is going on under the hood, so to speak, or what the engine can do."

The study results, which will appear in an upcoming issue of the Monthly Notices of the Royal Astronomical Society, also could provide new hints about how black holes produce particle jets.

"Though we don't definitely know the mechanism by which these jets are produced, our findings are supportive of the idea that magnetic field lines interact in a way that causes them to work like the elastic bands of a giant sling shot throwing incoming material back out from the black hole," Reynolds said.

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