Researchers at the University of Zurich have used a supercomputer to create the largest ever virtual universe, which is populated with some 25 billion galaxies generated from 2 trillion particles. The simulation will be used to calibrate Euclid, a satellite being developed by the European Space Agency that will be deployed in 2020 to investigate the nature of dark matter and dark energy.
The simulation represents the culmination of three years of work on the simulation's code by the Swiss researchers. After finishing the code, it was deployed for 80 hours on the Piz Daint supercomputer in Switzerland, the most powerful supercomputer in the world.
The simulated universe—which depicts the concentrations of dark matter known as "halos" that are thought to envelop most galaxies—is unprecedented in detail. As the researchers describe in their paper in Computational Astrophysics and Cosmology , the challenge was to simulate dark matter halos as small as a tenth of the size of the Milky Way in a volume that is the size of the observable universe. This was no small task, but it was a necessary one to calibrate Euclid, which will be observing similar objects IRL starting in 2020.
Cosmologists think that dark matter and energy make up about 23 percent and 72 percent of the universe, respectively. Yet despite their ubiquity, they are also some of the most mysterious substances in astrophysics.
"The nature of dark energy remains one of the main unsolved puzzles in modern science," said Romain Teyssier, a computational astrophysicist at the University of Zurich. The reason for this is that, as their names suggest, dark matter and dark energy cannot be observed with the naked eye—their presence is only known based on their interactions with baryonic, or visible, matter.
For this reason, cosmology is seeing a boom in dark energy research that uses supercomputers to model various aspects of dark matter and dark energy. So far, none of these simulations have held a candle to the complexity and detail of the recent Zurich simulation, which is also unique in that it will be used to calibrate a real space mission to study the dark universe.
Importantly, this simulation will also improve the quality and granularity of future simulations.
"The new time-to-solution of these simulations is a game changer as far as the way theory is used in cosmological measurements," the researchers wrote in their paper. "For the first time simulations will not only be used to help understand effects or to make some predictions, but will be needed to extract fundamental physical parameters from future survey data. They must become part of the data analysis pipelines."
Over the course of its six-year mapping mission, Euclid will look back 10 billion years in the Universe's history to help cosmologists better understand the role dark matter and energy played in shaping the universe and the galaxies that populate it.
It will be looking at the light from billions of galaxies and measuring minute distortions in the way this light travels to the satellite. It is this distortion that is the telltale sign that the light is being influenced by an invisible mass: dark matter.
Furthermore, the accelerated expansion of the universe is generally attributed to dark energy, although the mechanisms at work here are just beginning to be understood. By measuring the way light changes as the light source moves away from Euclid (an increase in wavelength known as redshift), cosmologists hope to gain insight in the role that dark energy plays in the expanding universe.
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