The early universe may have played a crucial role in the formation of supermassive black holes, but new research suggests that this process was not sustainable in the long term. The study, published in the arXiv preprint server, explores the idea that black holes grew rapidly during a specific period in the early universe, known as the cosmic dark age, but this growth was limited and not a permanent solution. This finding challenges the conventional understanding of black hole formation and highlights the need for alternative explanations.
Supermassive black holes, found at the centers of most galaxies, are incredibly massive, with some weighing more than 40 billion times the mass of the sun. The formation of these black holes has been a subject of debate, with theories suggesting they form through mergers over time. However, observations from the James Webb Space Telescope have revealed supermassive black holes that are too massive to be explained by mergers, existing when the universe was just half a billion years old.
The key to understanding this phenomenon lies in the Eddington Limit, which describes the maximum rate at which a black hole can grow. As matter is pulled towards a black hole, it becomes super-hot and high-pressure plasma, pushing distant matter away and slowing down the growth rate. The Eddington Limit sets the upper limit for black hole growth.
The research team, led by Ziyong Wu, created sophisticated hydrodynamic models to study black hole formation during the cosmic dark age. They discovered a 'super-Eddington period' where regions were dense enough to allow early black holes to grow at an accelerated rate, surpassing the Eddington Limit. However, this growth was only possible up to a certain mass, approximately 10,000 solar masses.
The study also revealed that this super-Eddington growth has limitations in the long run. Even black holes that grow at a sub-Eddington pace will eventually reach the same mass, just as a sprinter and a marathoner will have different performance peaks. This finding suggests that the super-Eddington growth cannot explain the massive black holes observed in the early universe.
Given that galactic mergers alone cannot account for these black holes, the researchers propose an alternative theory: seed mass black holes that formed very early, possibly during the inflationary period after the Big Bang. This hypothesis opens up new avenues for exploration, inviting further research into the origins of these enigmatic cosmic entities.
