News in Science

Supercomputer recreates the early cosmos

Sim Cosmos A team of Korean scientists have developed the largest computer simulation of the universe to replicate the web-like structure of an infant universe.

The simulations called Horizon Runs 2 and 3 were designed to reproduce the entire evolution of a universe made mostly of cold dark matter.

Developed by scientists led by Juhan Kim from the Korea Institute for Advanced Study in Seoul, the models involved up to 374 billion particles in a simulated area of ten gigaparsecs, roughly equivalent to about two-thirds the volume of the observable universe. A parsec is about 31 trillion kilometres.

Using the Korean Tachyon II supercomputer, the simulations ran for 20 days to see if they produced large scale structures similar to those in the real universe.

First galaxies

Scientists were looking for early evidence of galaxy formation and the development of galactic clusters and superclusters.

Writing in a paper published on the pre-press website ArXiv.org, Kim and colleagues report early signs of structures similar to the cosmic web pattern of cold dark matter, which form the foundation of the real universe.

They're hoping their simulations will eventually show "cold dark matter halo structures" that would later form into galaxies.

Kim and colleagues believe their simulation may also show evidence of baryon acoustic oscillations, which are large scale structures of waves comprising left over plasma, created when the universe was just 400,000 years old.

These waves became frozen in place as they cooled, and are now used as standard rulers to measure the expansion of the universe. The length of this standard ruler is currently about 150 megaparsecs.

To achieve this level of computational modelling Kim and colleagues used N-body simulations, which are dynamic computer models operating to specific rules such as the laws of physics.

Big, but lacks detail

Dr Claudio Gheller, a numerical cosmologist with ETH polytechnic in Zurich, says the simulation is the largest of its type, building on similar simulations.

"They're increasing the number of particles and the size of the box of the simulation," says Gheller.

He says unfortunately the simulation does not have enough resolution to see galaxy formation, because it is limited to studying the formation of big structures rather than the fine details of dark matter halos and galaxy formation.

"Other simulations are far more suitable for that, which have both the cold dark matter and the gas so you can describe what's happening more accurately and with more physics and more details," says Gheller.