The Formation of Intermediate Mass Black Holes in Galactic Nuclei
  Most stellar evolution models predict that black holes (BHs) should not exist
above approximately $50-70$ M$_\odot$. However, recent LIGO/Virgo detections
indicate the existence of BHs with masses at and above this threshold. We
suggest that massive BHs, including intermediate mass black holes (IMBHs), can
form in galactic nuclei through collisions between stellar-mass black holes and
the surrounding main-sequence stars. Considering dynamical processes such as
collisions, mass segregation, and relaxation, we find that this channel can be
quite efficient, forming IMBHs as massive as $10^4$ M$_\odot$. Our results
suggest that massive black holes and IMBHs may be ubiquitous in galactic
centres. This formation channel also has implications for observations.
Collisions between stars and BHs can produce electromagnetic signatures, for
example, from x-ray binaries and tidal disruption events. Additionally, formed
through this channel, both black holes in the mass gap and IMBHs can merge with
the supermassive black hole at the center of a galactic nucleus through
gravitational waves. These gravitational wave events are extreme and
intermediate mass ratio inspirals (EMRIs and IMRIs, respectively).
