Active galactic nuclei are supermassive black holes at the center of certain galaxies. As matter falls into these black holes, enormous amounts of energy are released, making active galactic nuclei, or AGN, one of the most energetic phenomena that can be observed in space. University of Arizona astronomers have now produced the sharpest direct images ever taken of an AGN in the infrared, using the Large Binocular Telescope Interferometer. 

Researchers from the Max Planck Institute for Astronomy in Germany were also involved in the study. The findings are published in the journal Nature Astronomy. 

"The Large Binocular Telescope Interferometer can be considered the first extremely large telescope, so it's very exciting to prove this is possible," said Jacob Isbell, a postdoctoral research associate at the U of A Steward Observatory and lead author of the Nature Astronomy paper. 

Certain galaxies have a supermassive black hole at the center. Some of them are considered active while others are inactive, depending on how quickly material is falling onto them, Isbell said. There's a disk around the black hole that glows more brightly the more material there is. If this accretion disk glows brightly enough, it's called an active supermassive black hole. The AGN that exists in galaxy NGC 1068, which neighbors the Milky Way, is one of the nearest that is considered active. 

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The Large Binocular Telescope is located on Mount Graham northeast of Tucson. It operates its two 8.4-meter mirrors independently, essentially functioning as two separate telescopes mounted side by side. The Large Binocular Telescope Interferometer combines the light from both mirrors, allowing for much higher resolution observations than would be possible with each mirror on its own. The interferometer makes the two mirrors act like a single telescope, producing high-quality images. This imaging technique has been successfully used in the past to study volcanoes on the surface of Jupiter's moon Io. The Io results encouraged the researchers to use the interferometer to look at an AGN. 

"The AGN within the galaxy NGC 1068 is especially bright, so it was the perfect opportunity to test this method," Isbell said. "These are the highest resolution direct images of an AGN taken so far."

The Large Binocular Telescope Interferometer Team is led by Steve Ertel, associate astronomer at Steward Observatory. Through the interferometer, the team was able to observe several cosmic phenomena going on simultaneously in the AGN. 

The bright disk around the supermassive black hole releases a lot of light, which pushes dust away like many tiny sails, a phenomenon known as radiation pressure. The images revealed a dusty, outflowing wind caused by radiation pressure. Simultaneously, farther out, there was a lot of material that was way brighter than it should be, if it was illuminated only by the bright accretion disk. By comparing the new images to past observations, the researchers were able to tie this finding to a radio jet that's blasting through the galaxy, hitting and heating up clouds of molecular gas and dust. Radio jet feedback is the interaction between powerful jets of radiation and particles emitted from supermassive black holes and their surrounding environment.

Direct imaging with extremely large telescopes such as the Larger Binocular Telescope Interferometer and the upcoming 83.5-foot Giant Magellan Telescope in Chile makes it possible to distinguish feedback from the radio jet and dusty wind simultaneously. Previously, the various processes were blended due to low resolution, but now it is possible to view their individual impact, Isbell said.

The study shows that the environments of AGN can be complex, and the new findings help scientists better understand AGN interactions with their host galaxies.

"This type of imaging can be used on any astronomical object," Isbell said. "We've already started looking at disks around stars or very large, evolved stars, which have dusty envelopes around them." 

Funding for the study came from the National Aeronautics and Space Administration through the Exoplanet Research Program under Grant No. 80NSSC21K0394 and the French Agence Nationale de la Recherche through the grant “AGN MELBa” ANR-21-CE31-0011.