Detecting supermassive galactic black holes that have been kickedout of their galaxies

Sometimes when galaxies merge, the supermassive black hole of one galaxy
doesn't merge with the other galaxy's black hole but instead it gets
kicked out of the system altogether. This is especially likely in the
case of a simultaneous three-way or higher galactic merger. A
"hypercompact stellar system" is the coterie of stars left attached to
and orbiting the kicked-out supermassive. There may be hundreds of these
objects floating around our galaxy, and they may have already been
detected in sky surveys but mistaken to be globular clusters. The speed
at which the stars orbit the supermassive may be a record of how fast
this supermassive was kicked out in the first place.

Yousuf Khan

New Kind Of Astronomical Object Around Black Hole: Living Fossil Records
'Supermassive' Kick
"“You can measure how big the kick was by measuring how fast the stars
are moving around the black hole,” says Merritt, professor of physics at
RIT. “Only stars orbiting faster than the kick velocity remain attached
to the black hole after the kick. These stars carry with them a kind of
fossil record of the kick, even after the black hole has slowed down. In
principle, you can reconstruct the properties of the kick, which is nice
because there would be no other way to do it.”"
http://www.sciencedaily.com/releases...0709170759.htm