Interactions in Dense Clusters

Best IMBH candidates are in clusters.

Heavier objects sink (binaries, BH,...).

Binaries have profound influence on dynamics.

Hard binaries harden: heat cluster.

Massive objects exchange into binaries.

Age $\ifmmode {\,\mathbin{\lower 3pt\hbox {$\,\rlap{\raise 8pt\hbox{$\char'074$}}\ma... ...{\raise 8pt\hbox{$\char'074$}}\mathchar''7218\,$}}} $}\fi {\rm few}\times 10^7$ yr; massive stars.

Might undergo direct collisions, mergers.

Binary energy injection $\Rightarrow$ $n$ is limited.

Binary-single encounters foster collisions.

Is collision rate high enough?

Age $\ifmmode {\mathbin{\lower 3pt\hbox {$\,\rlap{\raise 8pt\hbox{$\char'076$}}\math... ...pt\hbox {$\rlap{\raise 8pt\hbox{$\char'076$}}\mathchar''7218\,$}}} $}\fi 10^8$ yr; BH and NS.

Binary-single encounters.

$10\,M_\odot$ BH kicked out; $>50\,M_\odot$ BH stays.

Rates, efficiency?