Astronomers measure heaviest pair of supermassive black holes ever found

Using archival data from the Gemini North telescope, astronomers have measured the heaviest pair of supermassive black holes ever found.

Located within the elliptical galaxy B2 0402+379, the supermassive black hole binary is estimated to be 28 billion times that of our Sun. The measurement supports the long-standing theory that the mass of a supermassive binary black hole plays a key role in stalling a potential merger.

"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," says Martin Still, NSF program director for the International Gemini Observatory.

When two galaxies merge, their black holes can form a binary pair. While it's hypothesized that these binaries are destined to eventually merge, this phenomenon has never been directly observed. Despite evidence of supermassive black holes coming within mere light-years of each other, none have been able to overcome that final distance. The question of whether such an event is possible has been a topic of discussion amongst astronomers for decades.

A prevailing theory suggests that these systems are so massive that they deplete their host galaxy of the stellar material needed to drive their merger. This binary black hole in question provides strong evidence supporting this idea.

The team behind this study concluded that an exceptionally large number of stars would have been needed to slow the binary's orbit enough to bring them this close. In the process, the black holes seem to have ejected almost all the surrounding matter, leaving their galaxy's core depleted of stars and gas. With no more material available to further slow the pair’s orbit, their merger has stalled in its final stages.

Scientists are yet to determine whether the pair will overcome their stagnation and eventually merge on timescales of millions of years, or continue in orbital limbo forever. Considering that B2 0402+379's status as a fossil cluster - the result of an entire galaxy cluster’s worth of stars and gas merging into one single massive galaxy - it is unlikely that another galactic merger will occur.

"We're looking forward to follow-up investigations of B2 0402+379’s core where we’ll look at how much gas is present. This should give us more insight into whether the supermassive black holes can eventually merge or if they will stay stranded as a binary," says Tirth Surti, Stanford undergraduate and the lead author on the paper.