Supermassive Black Hole That Could Outshine a Galaxy Hidden Behind Cosmic Dust

Astronomers have discovered that a cloud of cosmic dust at the heart of the galaxy Messier 77 (M77) has been hiding a supermassive black hole, feeding and acting as an engine for powerful emissions.

Côte d'Azur Observatory astronomer Florentin Millour was part of a team led by Leiden University researcher Violeta Gámez Rosas, that made the discovery.

He told Newsweek: "Our team has obtained the best 'thermal' image ever obtained of the core of the active galaxy NGC1068, also known as M77.

"Thanks to this image, we can now better locate the inner massive black hole, which however remains hidden behind its surrounding dust environment."

The finding gives researchers a better insight into active galactic nuclei (AGNs) the central regions of some galaxies in which a supermassive black hole is surrounded by a thin disc of gas and dust—known as an accretion disc—that is slowly fed to its surface.

This process leads to powerful and energetic emissions from this central region and means that some AGNs can outshine all the stars in the entire galaxy that hosts them.

Bruno Lopez is the co-author of a paper detailing the team's findings published in the journal Nature. He told Newsweek: "AGNs are extremely powerful objects. They are actually the brightest light sources we know.

"Just imagine a black hole a billion times the mass of our sun tearing down matter in an overheated accretion disk, producing jets, winds, sublimating dust. It must really be hell living there.

"They rival the luminosity output of a whole galaxy on a tiny scale, comparable to the size of the solar system."

Millour, another co-author on the Nature paper, added that the findings also allowed the distribution of the dust to be visualized suggesting the black hole and its accretion disc in the AGN is surrounded by a bagel-shaped ring—or torus—of dust in which most of the energy is released.

Rescuing A 30-Year-Old Active Galactic Nuclei Model

AGNs come into different forms with some releasing bursts of radio waves and others shining brightly in visible light. Some like that of M77, located 47 million light-years away, are more subdued.

But a 30-year-old theory regarding these powerful galactic engines known as the Unified Model of AGNs suggests all AGNs consist of supermassive black holes surrounded by a thick ring of dust. This discovery helps confirm this model which has been recently challenged by other findings.

Gámez Rosas told Newsweek: "Very recent work had concluded that a ring
of hot dust around the black hole that was thin and tilted at an angle
where it should not be blocking the view to the black hole.

"This would have broken the Unified Model idea and required an ad hoc explanation of why we don't see the black hole region in this galaxy. This would be
a serious break with the understanding of AGNs that we have built up
over the last 30 years."

Côte d'Azur Observatory and University of Côte d'Azur researcher James Leftley, who is also an author of the paper, told Newsweek: "As M77 is the prototype of active galaxies, changing its nature put awkward pressure on the unified model, and propositions were made to simply discard it. Now we can say it still holds.

"However, we find that AGNs are far more complicated and chaotic than many assumed them to be."

The team arrived at their findings by using the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) to scan the center of M77. MATISSE takes infrared light collected by all four 27-foot telescopes of the Very Large Telescope (VLT)—situated in the Atacama desert region of Northern Chile—and combines it using a technique called interferometry.

Leftley explained: "Looking at the first reconstructed images coming out from MATISSE was a great surprise, as they were showing the expected brightness distribution of a nearly edge-on dusty torus. Our MATISSE images make it clear the black hole is hidden behind a huge screen of dust."

These new findings regarding M77's supermassive black hole could also help researchers better understand how galaxies change over time and how they were born, even those that don't currently have a feeding black hole.

Lopez told Newsweek: "We know that AGNs heavily influence the evolution of the galaxies that host them. They can affect the formation of stars and the growth of the supermassive black hole at the center of massive galaxies.

"Our own Milky Way has a supermassive black hole at its core and is thought to have been active long ago. Understanding AGN helps us to understand the formation process of galaxies, including our own."

Messier 77
An image of the galaxy Messier 77 with its shrouded supermassive black hole inset. Researchers discovered that the black hole was encircled by a dust torus confirming a 3 decade old model. Jaffe, Gámez-Rosas et al./ESO

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