Backward-Spinning Black Holes More Powerful

Oddball black holes that spin backward in the opposite direction of their surrounding debris discs appear to create more powerful jets of radiation than their regular-spinning brethren, a new study has found.

The finding could change scientists? understand of how galaxies evolve since the development of stars depends on the radiation ejected from the supermassive black holes anchoring their home galaxies.

A lot of what happens in an entire galaxy depends on what's going on in the miniscule central region where the black hole lies," said the study's lead author David Garofalo, a theoretical physicist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., in a statement.

The black holes can spin either in the same direction as the disks, called prograde black holes, or against the flow, called retrograde black holes. For decades, astronomers thought that the faster the spin of the black hole, the more powerful the jet. But there were problems with this "spin paradigm" model. For example, some prograde black holes had been found with no jets.

"Jets transport huge amounts of energy to the outskirts of galaxies, displace large volumes of the intergalactic gas, and act as feedback agents between the galaxy's very center and the large-scale environment," said Rita Sambruna, a researcher at NASA Goddard Space Flight Center, and an author of the new paper. "Understanding their origin is of paramount interest in modern astrophysics."

The scientists say that backward black holes shoot more powerful jets because there's more space between the black hole and the inner edge of its orbiting disk. This gap provides more room for the build-up of magnetic fields, which fuel the jets, an idea known as the Reynold's conjecture after the theoretical astrophysicist Chris Reynolds of the University of Maryland, College Park.

The new results showed that more distant radio-loud galaxies are powered by retrograde black holes, while relatively closer radio-quiet objects have prograde black holes. According to the study, the supermassive black holes evolve over time from a retrograde to a prograde state.

The research is detailed in the May 27 issue of the Monthly Notices of the Royal Astronomical Society.

"This new model also solves a paradox in the old spin paradigm," said theoretical astrophysicist David Meier, a researcher at JPL who was not involved in the study. "Everything now fits nicely into place."

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