Two supermassive black holes found in collision-created "fossil galaxies" are so massive that they refuse to collide and merge. The discovery could explain why, although supermassive black hole mergers are predicted theoretically, they have never been observed in progress.
The supermassive black hole system is located in elliptical galaxy B2 0402+379. Together, the two black holes have a joint mass that is 28 billion times larger than that of the sun, making this the most massive black hole binary ever seen. Not only that, but the binary components of this system are the closest in a supermassive black hole pair, separated by just 24 light-years.
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