Background and Motivation

Recent discoveries of these super-massive black holes located 13 billion light years away, corresponding to when the universe was just five per cent of its present age, pose a serious challenge to the theory of black hole formation and evolution. The physical mechanisms that form black holes and drive their growth are poorly understood. Theoretical studies have suggested these black holes formed from remnants of the first generation of stars, or from a direct gravitational collapse of a massive primordial gas cloud. However, these theories either have difficulty in forming super-massive black holes fast enough, or require very particular conditions.

Formation of monstrous black hole seed

The research term identified a promising physical process through which a massive black hole could form fast enough. The key was incorporating the effect of supersonic gas motions with respect to dark matter. The team’s super-computer simulations showed a massive clump of dark matter had formed when the universe was 100 million years old. Supersonic gas streams generated by the Big Bang were caught by dark matter to form a dense, turbulent gas cloud. Inside, a protostar started to form, and because the surrounding gas provided more than enough material for it to feed on, the star was able to grow extremely big in a short amount of time without releasing a lot of radiation.

Figure 1 – (Left) Projected density distributions of dark matter (background and top panel) and gas (bottom three panels) components when the massive star forms. [No caption image] [Movie: Density distributions of dark matter and gas components under the supersonic streaming motion (17MB)] (Right) Close up showing gas density distribution around a protostar (centre). The high-speed gas flowing from the top left of the image to the right compresses the central gas cloud. The part in yellow to light-green shows the development of strong turbulence. [No caption image]

Figure 2 – Evolution of the temperature and density structure during the protostellar accretion phase. The rapid accretion of a dense gas cloud (white contour) causes the brightening of the star, and photoionized regions are lauched (red). [No caption image] [Movie: Protostellar accretion phase (1.5MB)]

Origin of the distant supermassive black holes

Once reaching the mass of 34,000 times that of our Sun, the star collapsed by its own gravity, leaving a massive black hole. These massive black holes born in the early universe continued to grow and merge together to become a supermassive black hole. The number density of massive black holes is derived to be approximately one per a volume of three billion light-years on a side – remarkably close to the observed number density of supermassive black holes.

The result from this study will be important for future research into the growth of massive black holes. Especially with the increased number of black hole observations in the far universe that are expected to be made when NASA’s James Webb Space Telescope is launched next year.