Five new pairs of merging supermassive black holes have been discovered by combining data from NASA’s Chandra X-ray Observatory, the Wide-Field Infrared Sky Explorer Survey (WISE), and the ground-based Large Binocular Telescope in Arizona.
An artistic illustration of a binary black hole. Image credit: NASA / ESA / G. Bacon, STScI.
“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.
Because strong X-ray emission is a hallmark of growing supermassive black holes, the scientists then observed these systems with Chandra.
Closely-separated pairs of X-ray sources were found in five systems (SDSS J140737.17+442856.2, SDSS J012218.11+010025.7, SDSS J104518.03+351913.1, SDSS J122104.98+113752.3, and SDSS J130653.60+073518.1), providing compelling evidence that they contain two growing/feeding supermassive black holes.
Both the X-ray data from Chandra and the infrared observations, suggest that the supermassive black holes are buried in large amounts of dust and gas.
This graphic shows two of five new binary supermassive black holes recently identified by astronomers using a combination of data from NASA’s Chandra X-ray Observatory, the Wide-Field Infrared Sky Explorer Survey, and the Large Binocular Telescope. Image credit: NASA / CXC / George Mason University / University of Victoria / S. Satyapal et al / S. Ellison et al / SDSS / A. Hobart.
“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.”
“Our work shows that combining the infrared selection with X-ray follow-up is a very effective way to find these black hole pairs,” said University of Victoria astronomer Sara Ellison.
“X-rays and infrared radiation are able to penetrate the obscuring clouds of gas and dust surrounding these black hole pairs, and Chandra’s sharp vision is needed to separate them”.
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.
The other dual black hole was reported in a paper by Ellison et al, which was published in the September 2017 issue of the Monthly Notices of the Royal Astronomical Society.
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Shobita Satyapal et al. 2017. Buried AGNs in Advanced Mergers: Mid-infrared color selection as a dual AGN finder. ApJ, in press; arXiv: 1707.03921
Sara L. Ellison et al. 2017. Discovery of a dual active galactic nucleus with 8 kpc separation. MNRAS 470 (1): L49-L53; doi: 10.1093/mnrasl/slx076
