The lack of counterparts at other wavelengths indicates that the motion of CO-0.40-0.22 cannot be due to expansion driven by the death of massive stars in supernova explosions, or by the gravitational acceleration from a dense and massive cluster of stars. As a result, an intermediate-mass black hole (IMBH) is the most likely explanation for an invisible point-like mass with ~100,000 times the Sun’s mass. Such an IMBH could have formed through the runaway merger of massive stars at the center of a dense cluster of stars, or it was once the central black hole of a dwarf galaxy that got ingested by the Milky Way galaxy.
Tomoharu et al. (2015), “Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy”, arXiv:1512.04661 [astro-ph.GA]