The European Southern Observatory’s Very Large Telescope Interferometer (ESO’s VLTI) has observed a cloud of cosmic dust in the center of the galaxy Messier 77 that hides a supermassive black hole.

The findings, published in the journal Nature, have confirmed predictions made some 30 years ago and are giving astronomers new insight into ‘active galactic nuclei’, some of the brightest and most enigmatic objects in the universe.

Active galactic nuclei (AGN) are extremely energetic sources powered by supermassive black holes found at the center of some galaxies. These black holes feed on large volumes of cosmic gas and dust. Before being devoured, this material spirals towards the black hole, releasing enormous amounts of energy in the process, often dwarfing all the stars in the galaxy.

Astronomers have been curious about AGNs since they first saw these bright objects in the 1950s. Now, thanks to ESO’s VLTI, an international team of researchers, led by Violeta Gámez Rosas of Leiden University Basses), has taken a key step to understand how they work and what they are like up close.

Making extraordinarily detailed observations of the center of the galaxy Messier 77, also known as NGC 1068, Gámez Rosas and his team, which includes scientists from Austria, Germany, the Netherlands, France, the United States, Chile and Australia, detected a thick ring of cosmic gas and dust that hides a supermassive black hole. This discovery provides vital evidence to support a 30-year-old theory known as the Unified Model of AGN.

Astronomers know that there are different types of AGN. For example, some emit bursts of radio waves and some do not; some AGNs glow in visible light, while others, like Messier 77, are dimmer. The Unified Model asserts that, despite their differences, all AGNs have the same basic structure: a supermassive black hole surrounded by a thick ring of dust.

According to this model, any difference in appearance between the AGNs is a result of the orientation in which we view the black hole and its thick ring from Earth. The type of AGN we see depends on how much the ring obscures the black hole from our point of view, obscuring it completely in some cases.

Astronomers had already found some evidence to support the Unified Model, including the detection of hot dust at the center of Messier 77. However, questions remained as to whether this dust could completely hide a black hole, and thus explain why. this AGN glows less in visible light than others.

“The actual nature of the dust clouds and their role in both feeding the black hole and determining its appearance when viewed from Earth have been central questions in AGN studies for the past three decades,” explains Gámez. Rosas- Although no result will resolve all the questions we have, we have taken an important step in understanding how AGN works.”

The observations were made possible by the Multiple Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) mounted on ESO’s VLTI, located in the Atacama Desert, Chile. MATISSE combined the infrared light collected by the four 8.2-metre telescopes of ESO’s Very Large Telescope (VLT) using a technique called interferometry. The team used MATISSE to scan the center of Messier 77, located 47 million light-years away in the constellation Cetus.

“MATISSE can see a wide range of infrared wavelengths, allowing us to see through dust and accurately measure temperatures. As the VLTI is, in fact, a very large interferometer, we have the resolution to see what it occurs 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,” explains co-author Walter Jaffe, professor at Leiden University.

Combining changes in the dust’s temperature (from around room temperature to about 1,200°C) caused by the black hole’s intense radiation with absorption maps, the team built a detailed picture of the dust and pinpointed where the black hole should be. black.

The dust – in a thick inner ring and a larger disk – with the black hole at its center supports the Unified Model. The team also used data from the Atacama Large Millimeter/submillimeter Array, co-owned by ESO, and the National Radio Astronomy Observatory’s Very Long Baseline Array to build their image.

“Our results should lead to a better understanding of the inner workings of AGNs -concludes Gámez Rosas-. They could also help us better understand the history of the Milky Way, which harbors a supermassive black hole at its center that could have been active in the past”.

The researchers now want to use ESO’s VLTI to find more evidence to support the Unified Model of AGNs considering a larger sample of galaxies.

Team member Bruno López, MATISSE Principal Investigator at the Côte d’Azur Observatory in Nice, France, notes that “Messier 77 is an important AGN prototype and a wonderful motivation to expand our observing program and optimize MATISSE to address a broader sample of AGNs”.