An active supermassive black hole is one of the greatest wonders of the universe.

A dense, invisible object that could be billions of times the mass of our sun is surrounded by a massive, rippling disk and frame of material, glowing with light as it orbits toward the center of the black hole. But how big are these structures growing?

For the first time, an unmistakable detection of near-infrared light reveals the fringes of the supermassive accretion disk surrounding a supermassive black hole hundreds of millions of times the mass of our Sun, in a galaxy called III Zw 002, about 1.17 billion light-years away.

These discoveries, led by astronomer Dinemara Dias dos Santos of the National Institute of Space Research in Brazil, revealed the accretion disk about 52 light-days from the black hole. This measurement will allow for a better understanding of how supermassive black holes are fed.

It is difficult to reconstruct the material surrounding a black hole. Despite its size and the brilliance of the material around it, the distances between us and its galaxy mean it is still too small to resolve many details.

Since the material cannot be imaged directly, the light captured from the surrounding galaxy is analyzed for specific fingerprints that indicate the presence of an accretion disk.

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One of those signatures is what is known as a double peak in the emission spectrum. This occurs as a result of rotation. Emission is the light emitted when an excited atom loses energy. This energy manifests as a glow, the wavelength of which depends on the element of the atom.

Now, imagine an accretion disk around a black hole like a cylinder on a spinning disk. part of the disk is moving towards you; And the other part is moving away. The part of the disk that is moving towards us pushes the light so that the wavelengths are shortened; while the part that moves away extends it.

This means that the emission from a particular element appears at two wavelengths, resulting in a double peak in the spectrum.

Twin peaks around supermassive black holes have been detected before, but earlier detections originate from a point relatively close to the black hole, known as the narrow line region. This does not give much information about the full extent of the accretion disc.

Illustration showing the accretion disk around a black hole, and the double peak emission. (NOIRLab/NSF/AURA/P. Marenfeld)

Dias dos Santos and her colleagues found two double peaks, both of which were not from the narrow line region, but much further from the black hole, in what is known as the broad line region of the accretion disk.

This is the first detection of double peaks in the broadline region, and the first detection of double peaks using a near-infrared instrument.

“For the first time, the discovery of such double peak shapes places severe constraints on the geometry of the region that cannot be resolved otherwise,” says astrophysicist Alberto Rodríguez-Ardela of the National Astrophysical Laboratory in Brazil.

“And we now have clear evidence of the feeding process and the internal structure of the active galaxy.”

The double peaks, hydrogen on the left and oxygen on the right. (Dias dos Santos et al.,Astrophysical Journal Letters2023)

The first double peak, from the inner part of the bold region, was hydrogen. Modeling indicates that this was at a distance of 16.77 light-days from the black hole.

The second, the discovery of oxygen, was from the outskirts of the region, about 18.86 light-days away from the black hole. Modeling also indicates that the broad line region extends to a radius of 52.43 light-days from the black hole.

That is 9078 astronomical units. To be clear, Pluto is 40 astronomical units away from the sun.

This sounds huge, and it is to us, but it is somewhat consistent with attempts to measure the volume of accretion disks using light echoes bouncing off the inner edge of the torus, a volume that the researchers refer to in their paper as “compact”. .

The team will continue to monitor the galaxy to see if its continued behavior matches their expectations.

“This discovery gives us valuable insights into the structure and behavior of the broadline region in this particular galaxy, and highlights the fascinating phenomena that occur around supermassive black holes in active galaxies,” Rodriguez-Ardella said.

The research has been published in Astrophysical Journal Letters.

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