While close together in cosmological terms at just 750 light-years apart, or 6x the black hole sphere of influence, the supermassive black holes in the center of UGC 4211 won’t merge for a few hundred million years.
This artist’s conception shows the galaxy merger and its two central black holes. Image credit: ALMA / ESO / NAOJ / NRAO / M. Weiss, NRAO, AUI & NSF.
UGC 4211 is located some 480 million light-years away from Earth in the constellation of Cancer.
Also known as LEDA 22680, MCG +02-20-013 or SWIFT J0804.6+1045, the object is an ideal candidate for studying the end stages of galaxy mergers, which occur more frequently in the distant Universe, and as a result, can be difficult to observe.
In the new study, Eureka Scientific astronomer Michael Koss and his colleagues used the highly sensitive 1.3-mm receivers at the Atacama Large Millimeter/submillimeter Array (ALMA) to look deep into UGC 4211’s active galactic nuclei — compact, highly luminous areas in galaxies caused by the accretion of matter around central black holes.
They found not one, but two black holes gluttonously devouring the byproducts of the merger. Surprisingly, they were dining side-by-side with just 750 light-years between them.
“Simulations suggested that most of the population of black hole binaries in nearby galaxies would be inactive because they are more common, not two growing black holes like we found,” Dr. Koss said.
“The use of ALMA was a game-changer, and that finding two black holes so close together in the nearby Universe could pave the way for additional studies of the exciting phenomenon.”
“ALMA is unique in that it can see through large columns of gas and dust and achieve very high spatial resolution to see things very close together.”
“Our study has identified one of the closest pairs of black holes in a galaxy merger, and because we know that galaxy mergers are much more common in the distant Universe, these black hole binaries too may be much more common than previously thought.”
If close-paired binary black hole pairs are indeed commonplace, as the study authors posit, there could be significant implications for future detections of gravitational waves.
“There might be many pairs of growing supermassive black holes in the centers of galaxies that we have not been able to identify so far,” said Dr. Ezequiel Treister, an astronomer at Universidad Católica de Chile.
“If this is the case, in the near future we will be observing frequent gravitational wave events caused by the mergers of these objects across the Universe.”
The astronomers also analyzed data from NASA’s Chandra X-ray Observatory, the NASA/ESA Hubble Space Telescope, ESO’s Very Large Telescope, and the W. M. Keck Observatory.
“Each wavelength tells a different part of the story,” Dr. Treister said.
“While ground-based optical imaging showed us the whole merging galaxy, Hubble showed us the nuclear regions at high resolutions.”
“X-ray observations revealed that there was at least one active galactic nucleus in the system.”
“And ALMA showed us the exact location of these two growing, hungry supermassive black holes.”
“All of these data together have given us a clearer picture of how galaxies such as our own turned out to be the way they are, and what they will become in the future.”
“It’s important that with all these different images, you get the same story — that there are two black holes,” said Dr. Chiara Mingarelli, an astronomer with the Center for Computational Astrophysics at Flatiron Institute.
“This is where other studies of close-proximity supermassive black holes have fallen down in the past.”
“When people followed them up, it turned out that there was just one black hole.”
“This time we have many observations, all in agreement.”
The study appears in the Astrophysical Journal Letters.
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Michael J. Koss et al. 2023. UGC 4211: A Confirmed Dual Active Galactic Nucleus in the Local Universe at 230 pc Nuclear Separation. ApJL 942, L24; doi: 10.3847/2041-8213/aca8f0
