Starlight warped in the fabric of spacetime could help us find hidden black holes dancing together

An illustration of two black circles in the center of the screen separated by a red dot. There's a glowing blue circle around both black circles and a red semi-circle at the bottom.

Two supermassive black holes on a dizzying death spiral could soon become visible to astronomers after researchers worked out how, while rotating around each other, these dark, massive behemoths could gravitationally lens the stars behind them.

Pretty much every large galaxy hosts a supermassive black hole, ranging in mass from millions of times that of our sun (for example the black hole in our Milky Way galaxy, Sagittarius A*) to billions of solar masses. Ordinarily, galaxies have just one supermassive black hole at their hearts, but when two galaxies merge, their black holes can fall towards each other, eventually coming into each other's orbit and, long after that happens, merging in a burst of gravitational waves.