June 7, 2012

Black Holes Can Change Gears

Lee Rannals for

New research published in the journal Monthly Notices of the Royal Astronomical Society indicates that black holes are able to change gears, similar to an engine.

Black holes are able to swallow up matter, and return a lot of energy to the Universe in exchange for the mass they eat.

When a black hole attracts mass, they trigger the release of intense X-ray radiation and power strong jets.  However, scientists have been baffled because not all black holes do this the same way.

Researchers at the SRON Netherlands Institute for Space Research suggest that each black hole can change between two different regimes.

Black hole jets are like lighthouse-beams of material that race outwards close to the speed of light. They can have a major impact on the evolution of their environment.

Jets from the super-massive black holes found at the center of galaxies can blow huge bubbles and heat the gas found in clusters of galaxies. Black hole jets can also have an influence on Hanny's Voorwerp, which is a cloud of gas where stars form after being hit by the jet-beam of a black hole.

Astronomers in 2003 found that there is a connection between the X-ray emission from a black hole and its jet outflow. After this discovery, astronomers assumed that it was the same for all feeding black holes, until some of the cosmic objects showed a different behavior.

The unusual black holes still have a connection between energy released in the X-ray emission and that put in the jet ejection. However, the proportion is different from that in the "standard" black holes.

As more unusual black holes began to appear, it seemed as though there were two groups of black hole engines working in a slightly different way, until a later discovery.

A team led by Michael Coriat, found a black hole that switched between both X-ray and jet connection, depending on its brightness.

They found through this observation that black holes do not necessarily come with two different engines, but that each is able to run in two different regimes, like two gears of the same engine.

Peter Jonker and PhD-student Eva Ratti, two researchers from the SRON Netherlands Institute for Space Research,  have taken an important step forward in attempts to solve this puzzle by using X-ray observations from NASA's Chandra X-ray Observation.

The team used both Chandra and the Expanded Very Large Array in New Mexico and watched two black hole systems throughout their feeding frenzy.

"We found that these two black holes could also 'change gear', demonstrating that this is not an exceptional property of one peculiar black hole," Ratti said in a press release. "Our work suggests that changing gear might be common among black holes. We also found that the switch between gears happens at a similar X-ray luminosity for all the three black holes."

The new findings help provide new input to theoretical models that aim to explain both the functioning of the black hole engine, and its impact on the surrounding environment.