|Figure 16: Total number of black holes ejected in building up to a IMBH as a function
of seed mass. The four numbered curves are made assuming different cluster escape velocities. The
dotted line is 103 black holes, the assumed population for a young cluster. As can be seen, a very
large seed mass is necessary before IMBH formation by merging black holes becomes a possibility.
Image reproduced by permission from Gültekin et al. , copyright by IOP.