8th May 2014

Simulation recreates universe in unprecedented detail

A realistic "virtual universe" has been created, simulating 13 billion years of cosmic evolution at both large and small scales.

Researchers at MIT and the Harvard-Smithsonian Center for Astrophysics have generated the first realistic virtual universe using a computer simulation called "Illustris." This has recreated 13 billion years of cosmic evolution in a cube 350 million light years across with unprecedented resolution.

"Until now, no single simulation was able to reproduce the universe on both large and small scales simultaneously," says lead author Mark Vogelsberger who collaborated with researchers at several institutions, including the Heidelberg Institute for Theoretical Studies in Germany. The study is reported in the journal Nature.

Previous attempts to simulate the universe were hampered by a lack of computing power, along with complexities of the underlying physics. As a result, those programs were either limited in resolution, or forced to focus on a smaller portion of the universe. Earlier simulations also had trouble modelling complex feedback from star formation, supernova explosions, and supermassive black holes.

Illustris, however, employs a sophisticated computer program to recreate the evolution of the universe in high fidelity. This includes both normal matter and dark matter using 12 billion 3-D pixels.

The team dedicated five years to developing the Illustris program. The actual calculations took 3 months of "run time" – using a total of 8,000 CPUs running in parallel. If they had used an average desktop computer, the calculations would have taken over 2,000 years to complete.

The simulation began a mere 12 million years after the Big Bang. When it reached the present day, astronomers counted more than 41,000 galaxies in the cube of simulated space. Importantly, Illustris yielded a realistic mix of spiral galaxies like the Milky Way and football-shaped elliptical galaxies. It also recreated large-scale structures, like galaxy clusters, along with bubbles and voids of the cosmic web.

On the small scale, it accurately simulated the chemistries of individual galaxies. The smallest features it can model are roughly 1,000 light years across – about 1% of the Milky Way's diameter. Vogelsberger believes that 10 years from now, advances in computing power will make it possible to show features only a few light years across. Individual stars and planets would be much harder to simulate, due to the vast number of calculations required, though it should be possible eventually.

Since light travels at a fixed speed, the farther away astronomers look, the farther back in time they can see. A galaxy one billion light years away is seen as it was a billion years ago. Telescopes like Hubble can provide us with views of the early universe by looking to greater distances. However, astronomers can't use Hubble to follow the evolution of a single galaxy over time.

"Illustris is like a time machine. We can go forward and backward in time. We can pause the simulation and zoom into a single galaxy or galaxy cluster to see what's really going on," says co-author Shy Genel.

The video shown above morphs between different components of the simulation to highlight various layers – e.g. dark matter density, gas temperature and chemistry. A full resolution version is available to download here (right-click, save as). Several smaller videos and associated imagery have also been released at http://www.illustris-project.org/

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