Composite HST/NICMOS (left) and MUSE/X-IFU (right) FOV views of MG B2016+112.
Credit: arXiv (2026). DOI: 10.48550/arxiv.2609.31826
Credit: arXiv (2026). DOI: 10.48550/arxiv.2609.31826
Astronomers have found two actively feeding supermassive black holes separated by just 175 parsecs (570 light-years) in a galaxy seen when the universe was only about 2 billion years old. The system, MG B2016+112, lies at a redshift of 3.273 and is the most compact dual AGN known at this redshift. The study was posted to the arXiv preprint server on Sept. 25.
Black hole pairs
Models predict that galaxy mergers drive gas onto central supermassive black holes, so merging galaxies should sometimes host dual active galactic nuclei (AGN). Finding close pairs is hard because of observational limitations in distinguishing nearby bright spots.
Strong gravitational lensing is useful for observing these distant objects. It occurs when a massive galaxy between the object and observer warps spacetime so strongly that the background object's light is bent and magnified, producing multiple images, arcs or rings. By magnifying distant sources, it lets astronomers reconstruct the object and study it in depth.
This study, led by Jianghao Huyan and Júlia M. Sisk-Reynés, analyzes archival VLT/MUSE spectra of MG B2016+112, a radio-loud active galaxy at redshift 3.273 that is gravitationally lensed by a foreground galaxy into three images (say A, B and C). The team explores whether the system hosts one actively feeding black hole or two. Earlier radio and X-ray studies had suggested two, about 175 parsecs (around 570 light-years) apart. The current study conducted an independent test and made new measurements using spatially resolved optical spectra of all three images.
MUSE/X-IFU FOV views of MG B2016+112, showing the 5-pixel apertures the researchers integrated across to obtain the individual spectra of images A (left), B (center), and C (right). Credit: arXiv (2026). DOI: 10.48550/arxiv.2609.31826
The most compact duo
Using the archival MUSE data from 2018, they extracted spectral information for each of the three lensed images. They made corrections to remove absorption from our galaxy's gas. They also masked absorption from gas near the quasar.
Next, they measured the strengths of prominent emission lines—such as those from hydrogen, nitrogen, carbon and helium—that appeared in the three images. They found that most spectral lines were too affected by absorption to compare their ratios, but one ratio worked. The numbers matched for images A and B, while image C had a much lower value. This strongly suggested C is lit by a different black hole. "This provides strong spectroscopic evidence that C is associated with an ionizing source distinct from that producing A and B," the team writes in the paper.
They also estimated the black hole masses from the width of another line, C IV. All three estimates turned out to be in a similar mass range. The black hole associated with images A and B has an estimated mass of at least 20 to 23 million solar masses, whereas the one associated with C has an estimated mass of at least 15 million solar masses. Similar masses fit the idea of two similar galaxies having merged, each bringing its own black hole—"consistent with the interpretation that the host galaxy underwent a major merger," they explain.
Next, they measured the strengths of prominent emission lines—such as those from hydrogen, nitrogen, carbon and helium—that appeared in the three images. They found that most spectral lines were too affected by absorption to compare their ratios, but one ratio worked. The numbers matched for images A and B, while image C had a much lower value. This strongly suggested C is lit by a different black hole. "This provides strong spectroscopic evidence that C is associated with an ionizing source distinct from that producing A and B," the team writes in the paper.
They also estimated the black hole masses from the width of another line, C IV. All three estimates turned out to be in a similar mass range. The black hole associated with images A and B has an estimated mass of at least 20 to 23 million solar masses, whereas the one associated with C has an estimated mass of at least 15 million solar masses. Similar masses fit the idea of two similar galaxies having merged, each bringing its own black hole—"consistent with the interpretation that the host galaxy underwent a major merger," they explain.
Puzzling feeding pattern
The team also estimated the upper limits on the black holes' feeding rates. They found quite a difference between their feeding rates—estimates for A and B come out at about 47% and 51% of the maximum, while C is only about 4%. While this supports the dual-black-hole picture, it challenges simulations that predict the lighter black hole in a pair feeds faster: C is the lower-mass black hole and is feeding more slowly.
However, the team warns that the feeding rate for C could be uncertain, as it depends on the magnification, and the magnification they considered is only an average and may be off. The researchers call for near-infrared observations to check the masses independently.
For now, the results support the view that MG B2016+112 is a dual AGN, with images A and B from one source and image C from another. "At a projected separation of 175 pc at z = 3.273, this system represents the closest-separation confirmed dual AGN identified to date at such a high redshift," researchers conclude. The system provides a rare glimpse of black hole growth during a possible major galaxy merger in the early universe.
However, the team warns that the feeding rate for C could be uncertain, as it depends on the magnification, and the magnification they considered is only an average and may be off. The researchers call for near-infrared observations to check the masses independently.
For now, the results support the view that MG B2016+112 is a dual AGN, with images A and B from one source and image C from another. "At a projected separation of 175 pc at z = 3.273, this system represents the closest-separation confirmed dual AGN identified to date at such a high redshift," researchers conclude. The system provides a rare glimpse of black hole growth during a possible major galaxy merger in the early universe.
Source: Phys.org
Written for you by our author Shreejaya Karantha, edited by Lisa Lock, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.
Publication details
Jianghao Huyan et al., MUSE spectroscopy of the compact dual AGN in the z=3.273 radio-loud gravitational lens MG B2016+112, arXiv (2026). DOI: 10.48550/arxiv.2609.31826
Journal information: arXiv
