Headline: Spinning Black Holes Like Giant Batteries, Study ShowsResearchers have found a possible source for enigmatic high-energy particles called cosmic rays in a study that shows rapidly spinning black holes may act as giant batteries, shooting particles into the cosmos at nearly the speed of light.
The study involved four aged galaxies that used to be among the brightest beacons in the universe but are now somewhat worn out. These former quasars, as they would have been called, might help solve a longstanding mystery about cosmic rays.
The galaxies are above the handle of the Big Dipper and visible with backyard telescopes. Each contains a central black hole of at least 100 million solar masses that, if spinning, could fire off atomic particles at great speeds, the scientists said today at a joint meeting of the American Physical Society and the High Energy Astrophysics Division of the American Astronomical Society in Albuquerque, N.M.
The team includes Diego Torres of Princeton University and Elihu Boldt, Timothy Hamilton and Michael Loewenstein of NASA's Goddard Space Flight Center.
Quasar galaxies are thousands of times brighter than ordinary galaxies, fueled by a central black hole swallowing copious amounts of interstellar gas. The gas is sped up and superheated, triggering X-rays and other forms of radiation just before it is swallowed.
In galaxies with so-called quasar remnants, the black hole nucleus is no longer a strong source of radiation.
"Some quasar remnants might not be so lifeless after all, keeping busy in their later years," Torres said. "For the first time, we see the hint of a possible connection between the arrival directions of ultra-high energy cosmic rays and locations on the sky of nearby dormant galaxies hosting supermassive black holes."
Ultra high-energy cosmic rays represent one of astrophysics' greatest mysteries.
Each cosmic ray -- essentially a single sub-atomic particle such as a proton traveling just shy of light speed -- packs as much energy as a major league baseball pitch, over 40 million trillion electron volts. The particles' source must be within 200 million light-years of Earth, scientists have said, for cosmic rays from beyond this distance would lose energy as they traveled through the murk of cosmic microwave radiation pervading the universe.
Yet no one has been able to determine what kinds of objects within 200 million light-years could generate such energetic particles.
"The very fact that these four giant elliptical galaxies are apparently inactive makes them viable candidates for generating ultra high-energy cosmic rays," Boldt said, adding that drenching radiation from an active quasar would dampen cosmic-ray acceleration, sapping most of their energy.
The team concedes it cannot determine if the black holes in these galaxies are spinning, a basic requirement for a compact dynamo to accelerate ultra-high energy cosmic rays. Yet scientists have shown that it is possible. The prevailing theory is that supermassive black holes spin up as they accrete matter, absorbing orbital energy from the infalling matter.
Ultra-high-energy cosmic rays are extremely rare, striking the Earth's atmosphere at a rate about one per square kilometer per decade.
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