The study looked at hypervelocity stars, ones that are screaming through space at speeds far higher than stars around them. Some of these stars are moving so rapidly that they have reached galactic escape velocity; the Milky Way’s gravity can’t hold them. In the coming eons, they’ll flee the galaxy entirely. And we have good reason to believe these runaway stars were launched by SMBHs—but how?
Unrelated but I just had this Europa argument with someone at my Mutants and Masterminds (2e) game because I suggested it as a place for a hidden alien observation post.