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.
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