Researchers have discovered two supermassive black holes in collision-created “fossil galaxies” that are so massive they resist colliding and merging.

This finding may help explain why, despite theoretical predictions of supermassive black hole mergers, such events have not been observed in progress.

The binary supermassive black hole system is situated in the elliptical galaxy B2 0402+379, with a combined mass 28 billion times larger than that of the sun—making it the most massive black hole binary observed.

Remarkably, the binary components are the closest in a supermassive black hole pair, separated by just 24 light-years, Space.com is reporting.

Despite their proximity, the black holes seem to have been engaged in the same orbital dance for over 3 billion years without merging.

Written by B.C. Begley