The Direct Collapse of Supermassive Black Hole Seeds

Abstract

The direct collapse model of supermassive black hole seed formation requires that the gas cools predominantly via atomic hydrogen. To this end we simulate the effect of an anisotropic radiation source on the collapse of a halo at high redshift. The radiation source is placed at a distance of 3 kpc (physical) from the collapsing object and is set to emit monochromatically in the center of the Lyman-Werner (LW) band. The LW radiation emitted from the high redshift source is followed self-consistently using ray tracing techniques. Due to self-shielding, a small amount of H₂ is able to form at the very center of the collapsing halo even under very strong LW radiation. Furthermore, we find that a radiation source, emitting < 10⁵⁴ (∼10³ J₂₁) photons per second is required to cause the collapse of a clump of M ∼ 10⁵ M_⊙. The resulting accretion rate onto the collapsing object is ∼ 0.25 M_⊙ yr⁻¹. Our results display significant differences, compared to the isotropic radiation field case, in terms of H₂ fraction at an equivalent radius. These differences will significantly effect the dynamics of the collapse. With the inclusion of a strong anisotropic radiation source, the final mass of the collapsing object is found to be M ∼ 10⁵ M_⊙. This is consistent with predictions for the formation of a supermassive star or quasi-star leading to a supermassive black hole.