The Heaviest Supermassive Black Holes Ever Seen Weigh Billions More Than Our Sun

hero supermassive black hole pair noirlab
A team of astronomers has measured the heaviest pair of supermassive black holes ever detected. The measurements stem from archival data collected from NOIRLab’s Gemini North telescope on Manunakea in Hawaii.

Supermassive black holes have captured the imagination of astronomers and scientists since their initial discovery. Perhaps more intriguing, however, is a phenomenon that has been postulated, but has not been seen as of yet --  two supermassive black holes merging. A recently published a paper in The Astrophysical Journal may lend answers as to why this is.

The team used data from the Gemini North telescope in Hawaii operated by NOIRLab in order to analyze a supermassive black hole binary within the elliptical galaxy B2 04022+379. According to the National Optical-Infrared Astronomy Research Laboratory (NSF), this is the only binary pair to ever be resolved in enough detail to see both supermassive black holes separately. The binary pair also holds the record for having the smallest distance between them ever directly measured, 24 light-years. While the fact that these two mammoths are so close together should indicate they will eventually merge, further study has revealed that they have been stalled out at this distance for over three billion years.

To put the size of the binary’s enormous mass into perspective, they are estimated to be 28 billion larger than out Sun, making them the largest binary black hole ever measured. The measurement gives credence to a long-standing theory that the mass of a supermassive binary black hole plays an integral role in causing the pair to stall out before merging.

noirlab gemini north telescope
NOIRLab's Gemini North telescope in Hawaii.

“The data archive serving the International Gemini Observatory holds a gold mine of untapped scientific discovery,” remarked Martin Still, NSF program director for the International Gemini Observatory. “Mass measurements for this extreme supermassive binary black hole are an awe-inspiring example of the potential impact from new research that explores that rich archive.”

The new insights led the team to conclude that it would have taken an “exceptionally” large amount of stars to slow the binary’s orbit enough to bring them as close as they currently are. During the process, the pair of supermassive black holes apparently “flung out nearly all the matter in their vicinity,” leaving the core of the galaxy famished of stars and gas. This leads the group of astronomers to believe there is no more material available to further slow the pair’s orbit, thus stalling the merger in its final stages.

“Normally it seems that galaxies with lighter black hole pairs have enough stars and mass to drive the two together quickly,” explained Roger Romani, Stanford University physics professor and co-author of the paper. “Since this pair is so heavy it required lots of stars and gas to get the job done. But the binary has scoured the central galaxy of such matter, leaving it stalled and accessible for our study.”

The team is still uncertain of whether or not the pair of supermassive black holes will overcome their stagnation and eventually merge on timescales of millions of years, or if they will continue their celestial tango forever. If the pair do merge, NOIRLab says the resulting gravitational waves would be a hundred times more powerful than those produced by stellar-mass black hole mergers. It is also possible that the two could overcome their stalemate if another galaxy merges, giving the dynamic duo the additional material needed to finally come together.