Supercomputer turns the cosmic clock back

Astronomers have tested a method of reconstructing the state of the early universe by applying it to 4,000 simulated universes using the ATERUI II supercomputer at the National Astronomical Observatory of Japan (NAOJ). They found that the method, along with new observations, could place better constraints on inflation, one of the most enigmatic events in the history of the universe. The method can shorten the observation time to distinguish between different inflation theories.

Just after the universe came into being 13.8 billion years ago, it suddenly grew more than 1 trillion trillion times in less than a trillionth of a trillionth of a microsecond, but nobody knows how or why. This sudden inflation is one of the most important mysteries in modern astronomy. Inflation must have caused fluctuations in the excess density that would have affected the distribution of galaxy evolution. The mapping of the distribution of galaxies can therefore exclude inflation models that do not correspond to the observed data.

However, processes other than inflation also affect the distribution of galaxies, making it difficult to derive information about inflation directly from observations of the large-scale structure of the universe, the cosmic web that contains countless galaxies. In particular, the gravity-driven growth of groups of galaxies can obscure the fluctuations in density.

A research team led by Masato Shirasaki, an assistant professor at NAOJ and the Institute of Statistical Mathematics, has applied a reconstruction method to turn back the clock and remove gravitational effects from the large-scale structure. They used ATERUI II, the world’s fastest supercomputer dedicated to astronomy simulations, to create and develop 4,000 simulated universes through gravity-driven growth. Then they applied this method to see how well it reconstructs the initial state of the simulations. The team found that their method could correct the gravitational effects and improve the constraints on the over-density fluctuations.

“We found this method to be very effective,” says Shirasaki. “Using this method, we can verify inflation theories by about a tenth of the amount of data. This method can shorten the required observation time in upcoming missions of galaxies such as SuMIRe by NAOJ’s Subaru Telescope.”

These results appear as Masato Shirasaki et. al. “Limit Primordial Non-Gaussian with a Post-Reconstructed Galaxy Bispectrum in Redshift Space,” in Physical overview D on January 4, 2021.

Provided by Center for Computational Astrophysics