At the center of almost every galaxy, there’s a supermassive black hole – each millions, if not billions of times, the mass of our Sun. Their presence is important in regulating how galaxies change, and they are key to most theories of galaxy evolution. However, astronomers have an issue with them because they have discovered huge black holes already in place when the universe was still very young.
In a new paper published in Science, an international team of physicists have proposed a new mechanism for the rapid formation of supermassive black holes. The researchers suggest that primordial gas moving at supersonic speed inside large dark matter clumps could accumulate rapidly enough to turn into black holes.
"The study identified a promising physical process through which a massive black hole could form fast enough by only introducing supersonic gas motions left over the Big Bang. These massive black holes born in the early universe continued to grow to become a supermassive black hole," lead author Dr Shingo Hirano told IFLScience
The team ran a series of simulations to work out exactly what would happen under the condition they put forward. The starting point for their scenarios was clumps of dark matter 10 million times the mass of the Sun. As the gas falls towards the center of these “gravitational wells”, it begins to heat up and push back. The supersonic motion guarantees that enough mass is assembled when the cloud begins collapsing under its own weight.
At the center of the cloud a star forms. In just 2,000 years, the star will be 50 times the mass of the Sun – and it will continue to grow, reaching tens of thousand of times the mass of our star. In one scenario, the black hole formed was 34,000 times the mass of the Sun. If such a black hole could form about 100 million years after the Big Bang, then it could easily become billions of times the mass of the Sun in just a few hundred million years.
This scenario provides a solution for the discovery of a huge supermassive black hole already in place 770 million years after the Big Bang. However, this is not the only hypothesis that delivers large black holes from the dawn of the universe. Recently, it has been suggested that proto-galaxies could help with the formation of such objects. The new approach doesn’t need complex interactions, just a speedy gas collapse.
"Other hypotheses on the formation of SMBH in the early Universe resort to very particular conditions; e.g. nearby light source galaxy or super-Eddington growth. Whereas our scenario need only the supersonic gas streams which are intrinsically generated in the early Universe according to the standard model of structure formation," added Dr Hirano.
The formation of supermassive black holes is one of the great mysteries of the early universe, and hopefully soon we will be close to solving it.
