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Register a new userFormation of massive black holes via collisions and accretion
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Added by
Dominik R. G. Schleicher
Publication date
2018
fields
Physics
and research's language is
English
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To explain the observed population of supermassive black holes at z~7, very massive seed black holes or, alternatively, super-Eddington scenarios are needed to reach final masses of the order of 10^9 solar masses. A popular explanation for massive seeds has been the direct collapse model, which predicts the formation of a single massive object due to the direct collapse of a massive gas cloud. Simulations over the last years have however shown that such a scenario is very difficult to achieve. A realistic model of black hole formation should therefore take fragmentation into account, and consider the interaction between stellar-dynamical and gas-dynamical processes. We present here numerical simulations pursued with the AMUSE code, employing an approximate treatment of the gas. Based on these simulations, we show that very massive black holes of 10^4-10^5 solar masses may form depending on the gas supply and the accretion onto the protostars.
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Models aiming to explain the formation of massive black hole seeds, and in particular the direct collapse scenario, face substantial difficulties. These are rooted in rather ad hoc and fine-tuned initial conditions, such as the simultaneous requirements of extremely low metallicities and strong radiation backgrounds. Here we explore a modification of such scenarios where a massive primordial star cluster is initially produced. Subsequent stellar collisions give rise to the formation of massive (10^4 - 10^5 solar mass) objects. Our calculations demonstrate that the interplay between stellar dynamics, gas accretion and protostellar evolution is particularly relevant. Gas accretion onto the protostars enhances their radii, resulting in an enhanced collisional cross section. We show that the fraction of collisions can increase from 0.1-1% of the initial population to about 10% when compared to gas-free models or models of protostellar clusters in the local Universe. We conclude that very massive objects can form in spite of initial fragmentation, making the first massive protostellar clusters viable candidate birth places for observed supermassive black holes.
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