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. Astronomers at the University of Arizona have produced the highest-resolution 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 also participated 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 is very exciting to show that this is possible,” said Jacob Isbell, a postdoctoral research associate at the U of A’s Steward Observatory and lead author of the study. Nature Astronomy paper.
Every galaxy has a supermassive black hole at its center. Some of them are considered active while others are inactive, depending on how quickly the material falls on them, Isbell said. There is a disk around the black hole that shines brighter the more material there is. If this accretion disk shines bright enough, it is called an active supermassive black hole. The AGN that exists in the galaxy NGC 1068, neighboring the Milky Way, is one of the closest ones that are considered active.
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’s interferometer combines light from both mirrors, allowing observations with much higher resolution than would be possible with each mirror alone. This imaging technique has been used successfully in the past to study volcanoes on the surface of Jupiter’s moon Io. The Jupiter results encouraged researchers to use the interferometer to observe 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 interferometer team is led by Steve Ertel, associate astronomer at Steward Observatory. Through the interferometer, the team was able to observe several cosmic phenomena occurring simultaneously in the AGN.
The bright disk surrounding the supermassive black hole releases a lot of light, which pushes the dust like small candles, a phenomenon known as radiation pressure. The images revealed a dusty wind caused by radiation pressure. At the same time, further away, there was a lot of material that was much brighter than it should have been, considering it was illuminated only by the bright accretion disk. By comparing the new images with previous observations, the researchers were able to link this finding to a radio jet passing through the galaxy, hitting and heating clouds of gas and molecular dust. Radio jet feedback is the interaction between powerful jets of radiation and particles emitted by supermassive black holes and their surrounding environment.
Direct imaging with extremely large telescopes, such as the largest binocular telescope interferometer and the upcoming 83.5-foot Giant Magellan Telescope located in Chile, makes it possible to distinguish radio jet feedback and dusty wind simultaneously. Previously, the different processes were mixed together due to low resolution, but now it is possible to see their individual impact, Isbell said.
The study shows that AGN’s environments can be complex and the new findings help to better understand AGN’s interaction with its host galaxies.
“This type of imaging can be used on any astronomical object,” Isbell said. “We have already started to observe disks around stars or very large evolved stars, which have dust envelopes around them.”