Wednesday, November 29, 2023

Largest-ever computer simulation to investigate Universe’s evolution

An international team of astronomers has carried out what is believed to be the largest ever cosmological computer simulation, tracking not only dark but also ordinary matter to investigate how the Universe evolved.

The project, dubbed FLAMINGO (Full-hydro Large-scale structure simulations with All-sky Mapping for the Interpretation of Next Generation Observations), calculated the evolution of all components of the Universe – ordinary matter, dark matter, and dark energy – according to the laws of physics. As the simulation progresses, virtual galaxies and clusters of galaxies emerge.

Facilities such as ESA’s Euclid Space Telescope and NASA’s JWST (James Webb Space Telescope) collect impressive amounts of data on galaxies, quasars, and stars. Such simulations could play a key role in the scientific interpretation of the data by connecting predictions from theories of our Universe to the observed data.

According to the theory, the properties of our entire Universe are set by a few numbers called ‘cosmological parameters.’ These parameters can be measured by different methods, such as observing the cosmic microwave background (CMB), which is a faint background glow left over from the early Universe, or studying the lensing effect of galaxies, which is how their gravitational force bends light. However, these ‘tensions’ could signal the demise of the standard model of cosmology – the cold dark matter model.

The computer simulations may be able to reveal the cause of these tensions because they can inform scientists about possible sources of bias (systematic errors) in the measurements. So far, the computer simulations used to compare to the observations only track cold dark matter.

“Although the dark matter dominates gravity, the contribution of ordinary matter can no longer be neglected,” says research leader Joop Schaye from Leiden University, “since that contribution could be similar to the deviations between the models and the observations.”

The first results show that both neutrinos and ordinary matter are essential for making accurate predictions but do not eliminate the tensions between the different cosmological observations.

Normal matter, or baryonic matter, which makes up only 16% of all matter in the Universe, is more difficult to simulate and requires more computational power. This is because baryonic matter is affected by both gravity and gas pressure, which can result in matter being ejected from galaxies by active black holes and supernovae into intergalactic space.

The strength of these intergalactic winds depends on explosions in the interstellar medium and is hard to predict. Moreover, the role of neutrinos, subatomic particles with very small but uncertain mass, is also significant, but their motion has not been simulated so far.

The ambitious project embarked on a series of computer simulations tracking structure formation in dark matter, ordinary matter, and neutrinos. “The effect of galactic winds was calibrated using machine learning by comparing the predictions of lots of different simulations of relatively small volumes with the observed masses of galaxies and the distribution of gas in clusters of galaxies,” explains Ph.D. student Roi Kugel (Leiden University).

The FLAMINGO project leveraged a supercomputer to execute these simulations across different cosmic volumes and at different resolutions. They also changed the model parameters, such as the strength of galactic winds, the mass of neutrinos, and the cosmological parameters in simulations of slightly smaller but still large volumes.

The most extensive simulation involved 300 billion resolution elements in a cubic volume with edges of ten billion light years. This is likely the largest cosmological computer simulation with ordinary matter ever completed.

“To make this simulation possible, we developed a new code, SWIFT, which efficiently distributes the computational work over 30 thousand CPUs,” Matthieu Schaller from Leiden University said in the press release.

In addition to providing unprecedented visual insights into the Universe’s evolution, the FLAMINGO simulations open a new virtual window on the Universe that will help make the most of cosmological observations.