Evenly Matched: Magnetic Fields vs Black Holes' Pull

As it turns out, the magnetic fields of supermassive black holes have an unexpected presence, their strength evenly matching the gravitational force produced by the black hole, according to a team of scientists from the US Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany.

"This paper for the first time systematically measures the strength of magnetic fields near black holes," Alexander Tchekhovskoy said in a Berkeley Lab news release. "This is important because we had no idea, and now we have evidence from not just one, not just two, but from 76 black holes."

Tchekhovskoy's previous research suggested that a black hole could sustain a magnetic field that was as strong as its gravity, but there was not yet any observational data to back up the theory. If the two forces truly balanced each other out, a cloud of gas caught on top of the magnetic field would be spared the pull of gravity and instead levitate in place.

Their evidence came in the form of jets of gas, created from magnetic fields, which shoot away from supermassive black holes and produce radio emission.

"We realized that the radio emission from black holes' jets can be used to measure the magnetic field strength near the black hold itself," lead author Mohammad Zamaninasab explained.

Prior studies had collected radio-emission data from "radio-loud" galaxies using the Very Long Baseline Array, a vast network of US radio telescopes. Utilizing this pre-existing data, researchers behind the current study created radio-emission maps at different wavelengths. Shifts in jet features between different maps allow them to calculate the field strength near the black hole.

They found that the magnetic fields not only evenly matched the strength of a black hole's pull, but also they are roughly 10,000 times stronger than Earth's own magnetic field - forcing scientists to reevaluate their previous understanding of black holes.

"We need to go back and look at our models once again," Tchekhovskoy said.

The findings were published in this week's issue of the journal Nature.