June 5, 2014
Magnetic Fields Counteract The Forces Of Supermassive Black Holes
Brett Smith for redOrbit.com - Your Universe Online
A supermassive black hole sits at the center of most galaxies and a new study published in the journal Nature has found that super-powerful magnetic fields can have influence near and even counteract the forces of these black holes."This paper for the first time systematically measures the strength of magnetic fields near black holes," said study author Alexander Tchekhovskoy, an astronomer at the University of California, Berkeley. "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."
Computational models developed by Tchekhovskoy suggested that a black hole could sustain a magnetic field as powerful as its own gravitational forces. However, there was not enough observational evidence to back up this projection. With the two forces in equilibrium, a cloud of gas trapped on top of the magnetic field would not be affected by the draw of gravity and essentially levitate in position.
The study team was able to confirm the strength of this magnetic field using evidence from jets of gas that fire away from supermassive black holes. Created by magnetic fields, these jets generate a 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," said study author Mohammad Zamaninasab, a researcher at Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany.
Using previously collected radio-emission data from the Very Long Baseline Array, a vast network of radio telescopes in the United States, the study team created radio-emission maps at different wavelengths. Changes in jet characteristics between maps let them determine the field strength near the black hole.
The researchers discovered that that these magnetic fields can be as strong as a black hole's gravity, but that they are also similar in strength to those produced inside MRI machines, about 10,000 times greater than Earth’s magnetic field.
The study team said their results suggest a reevaluation of theories surrounding the behavior of black holes.
"The magnetic fields are strong enough to dramatically alter how gas falls into black holes and how gas produces outflows that we do observe, much stronger than what has usually been assumed," he said. "We need to go back and look at our models once again."
Scientists are currently watching a gas cloud edging closer to the supermassive black hole at the center of our Milky Way Galaxy in the hope of finding out how black holes can get so big.
“We know they are big, and we know they are out there — in vast numbers — but we aren’t sure in detail how they get their mass,” said Northwestern University’s Daryl Haggard, who has been closely watching the little cloud, called G2, approach the black holes, known as Sgr A*.
“Do they grow rapidly when they are young, like our kids do, or do they grow in fits and starts, whenever fuel becomes available? In watching the encounter between Sgr A* and G2 we may catch a massive black hole in the act of snatching its next meal,” she said.