The Astronomers find single supermassive black holes all over the Universe,” said George Mason University astronomer Shobita Satyapal.
“But even though we’ve predicted they grow rapidly when they are interacting, growing dual supermassive black holes have been difficult to find.”
Before this study fewer than 10 confirmed pairs of growing black holes were known from X-ray studies, based mostly on chance detections.
To carry out a systematic search, Dr. Satyapal and colleagues had to carefully sift through data from telescopes that detect different wavelengths of light.
Starting with the Galaxy Zoo project, the astronomers used optical data from the Sloan Digital Sky Survey (SDSS) to identify galaxies where it appeared that a merger between two smaller galaxies was underway.
From this set, they selected objects where the separation between the centers of the two galaxies in the SDSS data is less than 30,000 light years, and the infrared colors from WISE data match those predicted for a rapidly growing supermassive black hole.
Seven merging systems containing at least one supermassive black hole were found with this technique.
“Each pair contains two supermassive black holes weighing millions of times the mass of the Sun,” the astronomers said.
“These black hole couples formed when two galaxies collided and merged with each other, forcing their supermassive black holes close together.”
Four of the binary black holes were reported in a paper by Satyapal et al that was recently accepted for publication in the Astrophysical Journal.
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