Image of a galaxy simulation

Researchers create ‘time machine’ simulations of ancestor galaxy cities


University of Tokyo researchers have recreated the full life cycle of some of the largest collections of galaxies observed in the distant universe 11 billion years ago.

Cosmological simulations are crucial to studying how the universe came to be, but many do not typically match what astronomers observe through telescopes. Instead, they are often designed to mirror the real universe in a statistical sense.

Constrained cosmological simulations, on the other hand, are designed to directly reproduce the structures we actually observe in the universe. However, most existing simulations of this kind have only been applied to our local universe, until now.

A team of researchers from the Kavli Institute for the Physics and Mathematics of the Universe have developed a simulation that allows them to study the life cycle of ancestor galaxy cities, known as 'COSTCO' (COnstrained Simulations of The COsmos Field). The tool's findings have been published in Nature Astronomy.

Since light from the distant universe is only reaching Earth now, the galaxies which telescopes observe today are a snapshot of the past, leading the researchers to compare their simulation tool to a "time machine".

“It’s like finding an old black-and-white picture of your grandfather and creating a video of his life,” said project assistant professor Khee-Gan Lee.

In this sense, the researchers took snapshots of “young” grandparent galaxies in the universe and then fast-forwarded their age to study how clusters of galaxies would form. The light from galaxies the researchers used traveled a distance of 11 billion light years to reach the Earth.

“We wanted to try developing a full simulation of the real distant universe to see how structures started out and how they ended,” said Metin Ata, the lead author of the paper.

The researchers were interested in studying distant structures such as massive galaxy protoclusters, which are ancestors of present-day galaxy clusters before they could clump under their own gravity. They found current studies of distant protoclusters were sometimes oversimplified, meaning they were done with simple models and not simulations.

Another important reason why the researchers created COSTO was to test the standard model of cosmology, used to describe the physics of the universe. By predicting the final mass and final distribution of structures in a given space, researchers could unveil previously undetected discrepancies in our current understanding of the universe.

The most challenging aspect of the process, according to the team, was taking the large-scale environment into account.

“This is something that is very important for the fate of those structures, whether they are isolated or associated with a bigger structure. If you don’t take the environment into account, then you get completely different answers. We were able to take the large-scale environment into account consistently, because we have a full simulation, and that’s why our prediction is more stable,” said Ata.

Using COSTCO, the researchers were able to find evidence of three already published galaxy protoclusters and disfavor one structure. In addition, they were able to identify five more structures that consistently formed in their simulations. This includes the Hyperion proto-supercluster, the largest and earliest proto-supercluster known today that is 5,000 times the mass of our Milky Way galaxy, which the researchers found will collapse into a large 300-million light year filament.

Their work is already being applied to other projects, such as a study on the cosmological environment of galaxies, and research into the absorption lines of distant quasars. 

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