Recent observations from the Stratospheric Observatory for Infrared Astronomy (SOFIA) have shed light on why some black holes appear to be active, gobbling up material from their surroundings, while others seem dormant.
Using active galaxy, Cygnus A, as an example - the latest SOFIA data indicates that magnetic fields are trapping and confining dust near the center of the galaxy and feeding material in to the supermassive black hole at its centre.
The unified model, which attempts to explain the different properties of active galaxies, states that the core is surrounded by a doughnut-shaped dust cloud, called a 'torus'.
How this obscuring structure is created and sustained has never been clear, but the new results from SOFIA indicate that magnetic fields may be responsible for keeping the dust close enough to be devoured by the hungry black hole.
This could explain the differences between the black holes at the centre of active galaxies (like Cygnus A) and their less active cousins (like our own Milky Way): the presence or absence of a strong magnetic field around the black hole.
SOFIA was able to conjure these fundings thanks to its new instrument, called the High-resolution Airborne Wideband Camera-plus (HAWC+), which is sensitive to the infrared emissions from aligned dust grains.
This has proven to be a powerful technique to study magnetic fields and test a fundamental prediction of the unified model: the role of the dusty torus in the active-galaxy phenomena.
"It's always exciting to discover something completely new," said Enrique Lopez-Rodriguez, a scientist at the SOFIA Science Center, and the lead author on the report of this new discovery.
"These observations from HAWC+ are unique. They show us how infrared polarisation can contribute to the study of galaxies."
Recent observations of the heart of Cygnus A made with HAWC+ show infrared radiation dominated by a well-aligned dusty structure.
Combining these results with archival data from the Herschel Space Observatory, the Hubble Space Telescope and the Gran Telescopio Canarias, the research team found that this powerful active galaxy, with its iconic large-scale jets, is able to confine the obscuring torus that feeds the supermassive black hole using a strong magnetic field.
However, the scientists said more observations of different types of galaxies are necessary to get the full picture of how magnetic fields affect the evolution of the environment surrounding supermassive black holes.
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