AsianScientist (Jun. 22, 2020) – Computer simulations conducted by astrophysicists at Tohoku University, Japan, suggest that precursors of supermassive black holes grow by swallowing up both interstellar gas as well as smaller stars. These findings, published in the Monthly Notices of the Royal Astronomical Society, help to explain the large number of supermassive black holes observed today.
Almost every galaxy in the modern Universe has a supermassive black hole at its center. Their masses can sometimes reach up to ten billion times the mass of the Sun. However, their origin is still one of the great mysteries of astronomy.
A popular theory is the direct collapse model where primordial clouds of interstellar gas collapse under self-gravity to form supermassive stars which then evolve into supermassive black holes. But previous studies have shown that direct collapse only works with pristine gas consisting of only hydrogen and helium. Heavier elements such as carbon and oxygen change the gas dynamics, causing the collapsing gas to fragment into many smaller clouds which form small stars of their own rather than a few supermassive stars. Direct collapse from pristine gas alone can’t explain the large number of supermassive blackholes seen today.
Dr. Chon Sunmyon, a postdoctoral fellow at the Japan Society for the Promotion of Science and Tohoku University and his team used the National Astronomical Observatory of Japan’s supercomputer ATERUI II to perform long-term 3D high-resolution simulations to test the possibility that supermassive stars could form even in heavy-element-enriched gas. Star formation in gas clouds including heavy elements has been difficult to simulate because of the computational cost of simulating the violent splitting of the gas, but advances in computing power allowed the team to overcome this challenge. These new simulations make it possible to study the formation of stars from gas clouds in more detail.
Contrary to previous predictions, the research team found that supermassive stars can still form from heavy-element enriched gas clouds. As expected, the gas cloud breaks up violently and many smaller stars form. However, there is a strong gas flow towards the center of the cloud; the smaller stars are dragged by this flow and are swallowed-up by the massive stars in the center. The simulations resulted in the formation of a massive star 10,000 time more massive than the Sun.
“This is the first time that we have shown the formation of such a large black hole precursor in clouds enriched in heavy-elements. We believe that the giant star thus formed will continue to grow and evolve into a giant black hole,” said Chon.
This new model shows that not only primordial gas, but also gas containing heavy elements can form giant stars, which are the seeds of black holes.
“Our new model is able to explain the origin of more black holes than the previous studies, and this result leads to a unified understanding of the origin of supermassive black holes,” said Professor Kazuyuki Omukai of Tohoku University.
The article can be found at: Chon & Omukai (2020) Supermassive Star Formation via Super Competitive Accretion in Slightly Metal-enriched Clouds.
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Source: National Institutes of Natural Sciences; Photo: Chon Sunmyon.
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