Astronomers carry out the largest cosmic computer simulation ever

An international team of astronomers has carried out what is believed to be the largest cosmological computer simulation ever, tracking not only dark matter, but also ordinary matter (such as planets, stars and galaxies), giving us a glimpse into how the universe evolved.

Flamingo’s simulations calculate 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 galaxy clusters appear. three Leaves It has been published in Monthly Notices of the Royal Astronomical SocietyOne describes the methods, one presents the simulations, and the third examines how well the simulations reproduce the large-scale structure of the universe.

Facilities such as the European Space Agency’s (ESA) recently launched Euclid Space Telescope and NASA’s JWST are collecting huge amounts of data about galaxies, quasars and stars. Simulations like FLAMINGO play a key role in the scientific interpretation of data by linking predictions from theories of the universe to observed data.

According to the theory, the properties of our entire universe are determined by a few numbers called “cosmological parameters” (six of them in the simplest version of the theory). The values ​​of these parameters can be measured very accurately in different ways.

One such method relies on the properties of the cosmic microwave background (CMB), a faint background glow left over from the early universe. However, these values ​​do not match those measured by other techniques that rely on the way galaxies’ gravitational force bends light (lensing). These “tensions” could signal the demise of the standard model of cosmology, the cold dark matter model.

Computer simulations may be able to reveal the cause of these tensions because they can inform scientists of potential biases (systematic errors) in measurements. If none of these reasons are sufficient to explain the tensions, the theory is in real trouble.

Until now, the computer simulations used to compare to observations only track cold dark matter. “Although dark matter dominates gravity, the contribution of ordinary matter can no longer be neglected, because that contribution can be similar to deviations between models and observations,” says research leader Job Schaie (Leiden University).

The first results show that both neutrinos and ordinary matter are needed to make accurate predictions, but they do not eliminate tensions between different cosmological observations.

Simulations that also track ordinary baryonic matter (also known as baryonic matter) are more difficult and require much more computing power. That’s because ordinary matter — which makes up only sixteen percent of all matter in the universe — feels not only gravity but also gas pressure, which can cause matter to be blown out of galaxies by active black holes and supernovas far out into intergalactic space.

The strength of these intergalactic winds depends on explosions that occur in the interstellar medium, and they are very difficult to predict. Moreover, the contribution of neutrinos, subatomic particles with a very small mass but not precisely known, is also important but their motion has not yet been simulated.

Astronomers have completed a series of computer simulations to track the composition of the structure of dark matter, ordinary matter, and neutrinos. Ph.D. “The effect of the galactic wind was calibrated using machine learning, by comparing predictions from many different simulations of relatively small scale with observed galaxy masses and gas distribution in galaxy clusters,” explains student Roy Coghill (Leiden University).

The researchers simulated the model that best describes the calibration observations using a supercomputer at different cosmic sizes and with different resolutions. In addition, they varied model parameters, including the strength of the galactic wind, the mass of neutrinos, and cosmological parameters in simulations of slightly smaller but still large volumes.

The largest simulation uses 300 billion resolution elements (particles with the mass of a small galaxy) in a cube volume whose edges are ten billion light-years away. This is believed to be the largest cosmological computer simulation of ordinary matter ever. “To make this simulation possible, we developed a new code, SWIFT, which efficiently distributes the computational work over more than 30,000 CPUs,” said Matthieu Schaller of Leiden University.

FLAMINGO simulations open a new virtual window on the universe that will help make the most of cosmological observations. In addition, the large amount of (virtual) data creates opportunities to make new theoretical discoveries and test new data analysis techniques, including machine learning.

Using machine learning, astronomers can then make predictions for random hypothetical universes. By comparing them with observations of large-scale structure, they can measure the values ​​of cosmological parameters. Furthermore, they can quantify the corresponding uncertainties by comparison with observations that constrain the influence of galactic winds.