Astronomers using the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) on ESO’s Very Large Telescope Interferometer have spotted a dense, obscuring cloud of cosmic dust around a central black hole of the barred spiral galaxy Messier 77. This observation provides confirmation of the so-called unified model of active galactic nuclei.
Active galactic nuclei are extremely energetic regions at the center of some galaxies, thought to be powered by supermassive black holes.
The light emitted by such nuclei produces spectral features relating to the region from which the light is emitted.
Distinct spectra have been used to split active galactic nuclei into two categories: type 1 or type 2 objects.
However, the unified model suggests that this distinction arises because the line of sight may sometimes be obscured by a dusty torus-shaped cloud surrounding and feeding the central black hole.
Astronomers had found some evidence to support the unified model before, including spotting warm dust at the center of Messier 77.
However, doubts remained about whether this dust could completely hide a black hole and hence explain why this active galactic nucleus shines less brightly in visible light than others.
“The real nature of the dust clouds and their role in both feeding the black hole and determining how it looks when viewed from Earth have been central questions in studies of active galactic nuclei over the last three decades,” said Dr. Violeta Gámez Rosas, an astronomer at Leiden University.
“Whilst no single result will settle all the questions we have, we have taken a major step in understanding how active galactic nuclei work.”
In the new research, Dr. Gámez Rosas and her colleagues used the MATISSE instrument on ESO’s Very Large Telescope Interferometer (VLTI) to scan the center of Messier 77, a barred spiral galaxy located 47 million light-years away in the constellation of Cetus.
They also used data from the Atacama Large Millimeter/submillimeter Array (ALMA) and NRAO’s Very Long Baseline Array.
“MATISSE can see a broad range of infrared wavelengths, which lets us see through the dust and accurately measure temperatures,” explained Leiden University’s Professor Walter Jaffe.
“Because the VLTI is in fact a very large interferometer, we have the resolution to see what’s going on even in galaxies as far away as Messier 77.”
“The images we obtained detail the changes in temperature and absorption of the dust clouds around the black hole.”
Combining the changes in dust temperature caused by the intense radiation from the black hole with the absorption maps, the authors built up a detailed picture of the dust and pinpointed where the black hole must lie.
The dust — in a thick inner ring and a more extended disk — with the black hole positioned at its center supports the unified model.
“Our results should lead to a better understanding of the inner workings of active galactic nuclei,” Dr. Gámez Rosas said.
“They could also help us better understand the history of the Milky Way, which harbors a supermassive black hole at its center that may have been active in the past.”
“Messier 77 is an important prototype active galactic nucleus and a wonderful motivation to expand our observing program and to optimize MATISSE to tackle a wider sample of active galactic nuclei,” said MATISSE principal investigator Dr. Bruno Lopez, an astronomer at the Observatoire de la Côte d’Azur.
The findings were published in the journal Nature.
V. Gámez Rosas et al. 2022. Thermal imaging of dust hiding the black hole in NGC 1068. Nature 602, 403-407; doi: 10.1038/s41586-021-04311-7
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