New study: Two black holes “dining dangerously close together”

Data from W. M. Keck Observatory at Maunakea on Hawaiʻi Island was used in a new study of a pair of merging galaxies.

Scientists discovered two supermassive black holes growing simultaneously near the center of the newly coalescing galaxy, dubbed UGC 4211.

“These super-hungry giants are the closest together that scientists have ever observed in multiple wavelengths. What’s more, the new research reveals that binary black holes and the galaxy mergers that create them may be surprisingly common in the universe,” according to a press release from the W. M. Keck Observatory.

The new study was published in today’s issue of The Astrophysical Journal Letters and was presented in a press conference at the 241st meeting of the American Astronomical Society in Seattle, Washington.

UGC 4211 is located in the constellation Cancer and is approximately 500 million light-years away from Earth. Scientists say it 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.

“When scientists looked deep into the merger’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,” according to the release.

“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,” said Michael Koss, a senior research scientist at Eureka Scientific and the lead author of the study.

If close-paired binary black hole pairs are indeed common, as Koss and the team posit, there could be significant implications for future detections of gravitational waves, according to researchers.

“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. 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,” said Ezequiel Treister, an astronomer at Universidad Católica de Chile and a co-author of the research.

In addition to using Keck Observatory’s adaptive optics system, researchers also studied the galaxy merger with the Hubble Space Telescope, European Southern Observatory’s Very Large Telescope, Atacama Large Millimeter/submillimeter Array, NASA’s Chandra X-ray Observatory, and the Victor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory.

“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,” said Treister in the release.

So far, scientists have mostly studied only the earliest stages of galaxy mergers. The new research could have a profound impact on the understanding of the Milky Way’s own impending merger with the nearby Andromeda Galaxy, according to the observatory.

“The Milky Way-Andromeda collision is in its very early stages and is predicted to occur in about 4.5 billion years. What we’ve just studied is a source in the very final stage of collision, so what we’re seeing presages that merger and also gives us insight into the connection between black holes merging and growing and eventually producing gravitational waves,” said Koss.