Formation of Ultramassive Black Holes in Early Universe: Insights from Astrid Simulation
Supermassive black holes are extremely heavy objects found in the Universe. Their mass ranges from millions to billions of times that of the Sun, and their evolution is difficult to explain.
The higher mass range of ultramassive black holes is even more challenging to explain, especially those that existed early in the history of the Universe. These black holes have masses over 10 billion Suns, and they are not just theoretical. For example, J2157, a galaxy observed around 12.3 billion years ago, hosted a black hole of 34 billion solar masses, while S5 0014+81, a galaxy spotted some 12.1 billion years ago, had a 40 billion solar mass black hole.
It is impossible for these black holes to have become so large by simply feeding on material around them because the Universe was less than 10 percent of its current age. However, they exist, and a new simulation using a powerful supercomputer to model the early Universe has shown that they can exist without breaking our current cosmological models.
According to astrophysicist Yueying Ni of the Harvard-Smithsonian Center for Astrophysics (CfA), “We found that one possible formation channel for ultra-massive black holes is from the extreme merger of massive galaxies that are most likely to happen in the epoch of the ‘cosmic noon’.” This means that the collision and merger of two massive galaxies is a possible explanation for the formation of ultramassive black holes.
There are two ways that black holes can gain mass: slow growth by accretion and collision between two black holes. The latter method has been observed in recent years and results in a black hole that is just short of the combined mass of the pre-merger objects, with a small percentage of mass escaping as gravitational energy during the merger.
Ultramassive black holes are some of the largest objects in the Universe and are challenging to explain because of their massive size, which can range from millions to billions of times the mass of the Sun. Even more difficult to understand are the black holes in the higher mass range that existed early in the history of the Universe, such as those with masses over 10 billion suns. Some of these black holes have been observed in galaxies like J2157 and S5 0014+81, which had black holes of 34 billion solar masses and 40 billion solar masses, respectively.
It is hard to believe that these black holes could have grown to such enormous sizes in less than 10% of the current age of the Universe just by feeding on the material around them. Nevertheless, these black holes exist. A new simulation, using a powerful supercomputer to model the early Universe, has provided a means of explaining how they could exist without breaking our current cosmological models.
Astrophysicist Yueying Ni of the Harvard-Smithsonian Center for Astrophysics (CfA) and her colleagues used specially developed software called Astrid to study the evolution of the Universe, including galaxy formation and mergers of supermassive black holes. They ran the software on a supercomputer called Frontera at the Texas Advanced Computing Center to determine how ultramassive black holes could form in the early Universe.
By using the Astrid simulation, the researchers found that around 10 billion years ago, ultramassive black holes of around 10 billion solar masses were forming. The researchers discovered three ultramassive black holes that assembled their mass during the cosmic noon, which is the time 11 billion years ago when star formation, active galactic nuclei (AGN), and supermassive black holes in general reach their peak activity.
During the cosmic noon epoch, the team observed an extreme and relatively fast merger of three massive galaxies. Each galaxy had a mass ten times that of the Milky Way, and a supermassive black hole was present at the center of each galaxy. The researchers found that these quasar triplet systems may be the progenitor of rare ultra-massive black holes that form after the triplets gravitationally interact and merge with each other.
Galaxies can collide and merge with each other, which can also occur in the early Universe. When this happens, the supermassive black holes at the centers of the galaxies will also merge, eventually forming a massive black hole. This can lead to high-mass quasars, a class of galaxies with a hyperactive supermassive black hole at the center that consumes vast amounts of material and blazes with light across billions of light-years, making them the brightest objects in the Universe.
However, we do not know how frequently these collisions occur because the gravitational waves they emit are too low for our current detection range. Despite this, estimates suggest that they happen quite often. Overall, the Astrid simulation showed that ultramassive black holes can form in the early Universe through the merging of massive galaxies and their supermassive black holes, providing a plausible explanation for their existence.
Recent technological advancements could bring us closer to finding observational evidence of mergers between ultramassive black holes. NASA’s upcoming space-based Laser Interferometer Space Antenna (LISA) will have the capability to detect a wider range of gravitational waves, and the James Webb Space Telescope is currently studying the distant Universe to uncover its secrets.
The team’s findings and the Astrid simulations could assist scientists in better understanding the observations made by the James Webb Space Telescope, and help to reveal how the cosmic noon era contributed to the formation of the Universe we observe today.
Ni and her team believe that this is an exciting time for astrophysicists, as these new discoveries could potentially shed more light on the formation and evolution of ultramassive black holes in the early Universe.
The research has been published in The Astrophysical Journal Letters.
https://iopscience.iop.org/article/10.3847/PSJ/acbb6b
