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Pairs of supermassive black holes spotted in colliding galaxies

We know that our universe is full of black holes, existing everywhere from between ancient strange clusters of stars to the massive black hole at the center of the Milky Way. Now astronomers from the Swiss Federal Institute of Technology (ETH) in Zurich have discovered several pairs of supermassive black holes located at the center of galaxies which are colliding together.

The scientists were examining what happens when two galaxies merge together into one larger galaxy. The process of collision generates huge amounts of gas and dust around the cores of the galaxies, which makes it difficult to see what is happening within. But the scientists were able to identify two supermassive black holes at the center of the two original galaxies which are drawing closer together and which will eventually coalesce into one enormous black hole.

The team used images from the W.M. Keck Observatory in Hawaii and NASA’s Hubble Space Telescope to survey nearby galaxies and to find pairs of galaxies which were merging. In total, they looked at 385 galaxies from the archive of Hubble images and 96 galaxies from the Keck telescope. Using Hubble images, they were able to identify galaxy NGC 6240, whose two cores have nearly melded and which could be seen through infrared light which pierces the dust and gas around the central core. Four other merging galaxies were also discovered from the Keck Observatory data, which used near-infrared light and adaptive optics to identify merging galaxies.

Overall, the findings suggest that more than 17% of the galaxies that they studied had a pair of black holes at their center which were spiraling closer and closer together. Eventually, all of these pairs of black holes will come together to form an even larger black hole, which should happen in the next 10 million years. That might sound like a long time, but in cosmic terms it’s very soon.

“This is the first large systematic survey of 500 galaxies that really isolated these hidden late-stage black hole mergers that are heavily obscured and highly luminous,” lead researcher Dr. Michael Koss told Science News. “It’s the first time this population has really been discovered. We found a surprising number of supermassive black holes growing larger and faster in the final stages of galaxy mergers.”

The findings are published in Nature.

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