Supermassive Black Hole Uses Magnetic Field To Snack On Cosmic Donut

Artist’s conception of the core of Cygnus A, including the dusty donut-shaped surroundings. NASA/SOFIA/Lynette Cook

At the center of almost every galaxy, there is a supermassive black hole. But not all of these cosmic juggernauts are actively feeding and creating powerful jets of material. It is unclear what goes on around these objects, but researchers have uncovered evidence suggesting magnetic fields could play a key role.

As reported in The Astrophysical Journal Letters, researchers used the airborne Stratospheric Observatory for Infrared Astronomy, or SOFIA, to study Cygnus A, a radio galaxy 757 million light-years away. Cygnus A sports a supermassive black hole responsible for the creation of massive jets of material, each extending for about 150,000 light-years.

SOFIA was recently equipped with a new instrument, the High-resolution Airborne Wideband Camera-plus (HAWC+), and with that was able to study the dusty donut of material around the supermassive black hole. And it observed, for the first time, how the magnetic field strongly affects this region.

The dust in the donut emits light in infrared and this emission appears to be polarized, meaning that the electromagnetic waves are all oscillating in the same plane. For the researchers, this was a telltale sign of a strong magnetic field. The material around the black hole is all roughly pointing in the same direction.

“It’s always exciting to discover something completely new,” lead author Enrique Lopez-Rodriguez, a scientist at the SOFIA Science Center, said in a statement. “These observations from HAWC+ are unique. They show us how infrared polarization can contribute to the study of galaxies.”

Two images of Cygnus A layered over each other to show the galaxy’s jets glowing with radio radiation (shown in red) and the core of the galaxy, plus some foreground stars and background objects from optical light (shown in yellow). Optical Image: NASA/STSiC Radio Image: NSF/NRAO/AUI/VLA

The findings are a big help for astronomers studying supermassive black holes. While it appears that many configurations of these objects can exist at the center of galaxies, researchers have come up with a unified model that encompasses all the variations. The observation from Cygnus A supports the unified model, making the magnetic field an integral regulator of how and when supermassive black holes feed.

More evidence is necessary to confirm if the unified model is correct, either completely or in part. Researchers could use SOFIA to test this further. They could look at both active and quiet supermassive black holes and study the strength of the magnetic field in both. If it’s much stronger in active galaxies, it would be an important confirmation of the unified model.  

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