We might actually witness this: https://www.sciencealert.com/a-pair-of-supermassive-black-holes-could-be-fated-to-collide-within-3-years
We might actually witness this: https://www.sciencealert.com/a-pair-of-supermassive-black-holes-could-be-fated-to-collide-within-3-years