Rapid formation of massive black holes in close proximity to embryonic protogalaxies

The appearance of supermassive black holes at very early times 1 – 3 in the Universe is a challenge to our understanding of star and black hole formation. The direct-collapse 4 , 5 black hole scenario provides a potential solution. A prerequisite for forming a direct-collapse black hole is that the formation of (much less massive) population III stars be avoided 6 , 7 ; this can be achieved by destroying H 2 by means of Lyman–Werner radiation (photons of energy around 12.6 eV). Here we show that two conditions must be met in the protogalaxy that will host the direct-collapse black hole. First, prior star formation must be delayed; this can be achieved with a background Lyman–Werner flux of J BG ≳ 100 J 21 ( J 21 is the intensity of background radiation in units of 10 −21 erg cm −2 s −1 Hz −1 sr −1 ). Second, an intense burst of Lyman–Werner radiation from a neighbouring star-bursting protogalaxy is required, just before the gas cloud undergoes gravitational collapse, to suppress star formation completely. Using high-resolution hydrodynamical simulations that include full radiative transfer, we find that these two conditions inevitably move the host protogalaxy onto the isothermal atomic cooling track, without the deleterious effects of either photo-evaporating the gas or polluting it with heavy elements. These atomically cooled, massive protogalaxies are expected ultimately to form a direct-collapse black hole of mass 10 4 −10 5 M ⊙ . The key ingredients for a massive cloud of gas to collapse and directly form a black hole without fragmenting and forming stars are a strong ionizing background emission and a closely timed burst of star formation in its vicinity.