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We explore here an scenario for massive black hole formation driven bystellar collisions in galactic nuclei, proposing a new formation regime ofglobal instability in nuclear stellar clusters triggered by runaway stellarcollisions. Using order of magnitude estimations, we show that observed nuclearstellar clusters avoid the regime where stellar collisions are dynamicallyrelevant over the whole system, while resolved detections of massive blackholes are well into such collision-dominated regime. We interpret this resultin terms of massive black holes and nuclear stellar clusters being differentevolutionary paths of a common formation mechanism, unified under the standardterminology of being both central massive objects. We propose a formationscenario where central massive objects more massive than $\rm \sim 10^8 \,Msun$, which also have relaxation times longer that their collision times, willbe too dense (in virial equilibrium) to be globally stable against stellarcollisions and most of its mass will collapse towards the formation of amassive black hole. Contrarily, this will only be the case at the core of lessdense central massive objects leading to the formation of black holes with muchlower black hole efficiencies $\rm \epsilon_{BH} = \frac{M_{BH}}{M_{CMO}}$,with these efficiencies $\rm \epsilon_{BH}$ drastically growing for centralmassive objects more massive than $\rm \sim 10^7 \, Msun$, approaching unityaround $\rm M_{CMO} \sim 10^8 \, Msun$. We show that the proposed scenariosuccessfully explains the relative trends observed in the masses, efficiencies,and scaling relations between massive black holes and nuclear stellar clusters.

Observational Support for Massive Black Hole Formation Driven by Runaway Stellar Collisions in Galactic Nuclei