Formation of the First Supermassive Black Holes

TLDR

We consider the physical conditions under which supermassive black holes could have formed inside the first galaxies, noting that fragmentation into stars is suppressed without substantial H₂ cooling. Our simulations follow the condensation of ~5 × 10⁶ M☉ around the two centers of the binary down to a scale of ≲0.1 pc. Our smoothed particle hydrodynamics simulations indicate that metal‑free galaxies with a virial temperature of ~10⁴ K and suppressed H₂ formation tend to form a binary black hole system containing ≳10 % of the host galaxy’s baryonic mass, while low‑spin galaxies form a single black hole instead, and these early black holes can trigger quasar activity before reionization, and primordial black hole binaries would emit gravitational radiation at z ≳ 10 detectable by LISA.

Abstract

We consider the physical conditions under which supermassive black holes could have formed inside the first galaxies. Our smoothed particle hydrodynamics simulations indicate that metal-free galaxies with a virial temperature of ~104 K and suppressed H2 formation (due to an intergalactic UV background) tend to form a binary black hole system that contains a substantial fraction (≳10%) of the total baryonic mass of the host galaxy. Fragmentation into stars is suppressed without substantial H2 cooling. Our simulations follow the condensation of ~5 × 106 M☉ around the two centers of the binary down to a scale of ≲0.1 pc. Low-spin galaxies form a single black hole instead. These early black holes lead to quasar activity before the epoch of reionization. Primordial black hole binaries lead to gravitational radiation emission at redshifts z ≳ 10 that would be detectable by Laser Interferometer Space Antenna.