Astronomers have just unveiled an incredible new tool to answer some of the most complex questions about how galaxies form. The team used Illustris TNG50 – the "most detailed large-scale simulation of the cosmos yet." The first results indicate there is a crucial interplay between cosmic gas flows and galactic structures, something we are unable to learn from observations alone.

The simulation is a “universe in a box,” whereby researchers put in the necessary rules and ingredients and then let it evolve. The findings, reported in the Monthly Notices of the Royal Astronomical Society, are particularly important for the formation of spiral galaxies.

Starting from messy clumps of gas, thin disks typical of spiral galaxies naturally emerge in the simulation. As time goes by, chaotic clumps settle into orderly spirals and the inflow of gas produces stars in the disk in an ordered circular orbit.

“In practice, TNG50 shows that our own Milky Way galaxy with its thin disk is at the height of galaxy fashion: over the past 10 billion years, at least those galaxies that are still forming new stars have become more and more disk-like, and their chaotic internal motions have decreased considerably,” co-lead of the team Dr Annalisa Pillepich, from the Max Planck Institute for Astronomy, said in a statement. “The Universe was much more messy when it was just a few billion years old!”

The simulation is a cube of space 230 million light-years across, with the researchers capable of tracking its evolution at a scale a million times smaller. They started with 20 billion particles that represent clumps of dark matter and regular matter over a simulated time equivalent to the age of the universe. In this cosmic cube, researchers track thousands of galaxies as they evolved and changed over the age of the universe. 

“Numerical experiments of this kind are particularly successful when you get out more than you put in. In our simulation, we see phenomena that had not been programmed explicitly into the simulation code. These phenomena emerge in a natural fashion, from the complex interplay of the basic physical ingredients of our model universe,” explained Dr Dylan Nelson, from the Max Planck Institute for Astrophysics.

The formation of spirals was one of the emergent phenomena. Another was the production of gas outflows from galaxies. As gas is released by supernovae and supermassive black holes, it slows down and can fall back in, accelerating the formation of the thin disks.

To run the simulation on a single processor would have taken 15,000 years. Instead, the team used 16,000 processor cores from the Hazel Hen supercomputer in Stuttgart, Germany, making it the most demanding computational cosmological simulation to date. All the data from the simulation will be released to the public, and the team hopes that many more emergent phenomena will be discovered in the TNG50.