Has the standard cosmological model been broken or just cracked

Has the standard cosmological model been broken or just cracked
by Robert Schreiber
Berlin, Germany (SPX) Jul 20, 2023

A global consortium of astrophysicists spearheaded by teams from the Max Planck Institute for Astrophysics in Germany, Harvard University in the United States, and Durham University in the United Kingdom, have taken a bold stride towards understanding the cosmos. The team has recently simulated the formation of galaxies and cosmic structures across vast expanses of space.

A unique aspect of their simulation is the inclusion of enigmatic neutrino particles, potentially providing valuable data about their mass. The preliminary outcomes of this venture, coined "MillenniumTNG," were featured in a series of ten articles in the Monthly Notices of the Royal Astronomical Society. These fresh computations serve to examine the accuracy of the standard cosmological model, paving the way for interpreting upcoming cosmological observations more precisely.

Over the years, cosmologists have grown accustomed to the peculiar notion that our universe's matter composition is primarily influenced by the elusive dark matter. Moreover, an even more baffling concept suggests the presence of an enigmatic dark energy field, which appears to counteract gravity and accelerates cosmic expansion. Normal baryonic matter, the building blocks for stars and planets, only constitutes less than 5% of the cosmic mixture.

This cosmological model, known as Lambda-Cold Dark Matter (LCDM), has proven remarkably consistent with a vast spectrum of observational data, from the cosmic microwave radiation - the residual heat from the Big Bang - to the intricate arrangement of galaxies along a vast network of dark matter filaments, known as the "cosmic web." Despite the model's efficacy, the actual physical essence of dark matter and dark energy remains elusive, prompting astrophysicists to explore potential inconsistencies in the LCDM theory, which may shed light on these universal enigmas.

Researchers from Max Planck Institute for Astrophysics, along with international collaborators, have made a significant stride in tackling this challenge. Leveraging their prior successes in the "Millennium" and "IllustrisTNG" projects, the team designed an advanced set of simulation models, termed "MillenniumTNG." These models allow a detailed prediction of the LCDM model implications with a greater level of statistical precision than ever before.

The team utilized the advanced cosmological code GADGET-4 to calculate the most extensive high-resolution dark matter simulations to date, spanning nearly 10 billion light-years. Additionally, they deployed the moving-mesh hydrodynamical code AREPO to follow galaxy formation processes in vast spaces, representing the universe as a whole. This dual-simulation approach allowed the team to precisely assess the impact of baryonic processes such as supernova explosions and supermassive black holes on the overall matter distribution.

Furthermore, they factored in the effects of massive neutrinos in their simulations, an unprecedented move in such large-scale cosmic simulations. This addition is expected to help decipher neutrino mass, a lingering question in particle physics, using the data from forthcoming cosmological surveys.

For these ambitious simulations, the research team employed two high-powered supercomputers: the SuperMUC-NG at the Leibniz Supercomputing Centre in Garching, and the Cosma8 hosted by Durham University. Over 120,000 computer cores worked tirelessly for nearly two months on the SuperMUC-NG to render the most comprehensive hydrodynamical simulation model yet. MillenniumTNG follows the formation of around one hundred million galaxies across a region of the universe stretching approximately 2400 million light-years, a calculation about 15 times larger than the previous best, the TNG300 model.

The initial results of the MillenniumTNG project underscore the significant role of computer simulations in modern cosmology. The team submitted ten introductory scientific papers for the project, eight of which have appeared in the MNRAS, with the remaining two set to be published soon. One of the studies explores the orientations of galaxies, highlighting an unexpected correlation in their shapes' alignment over random pointing.

PhD student Ana Maria Delgado from the MillenniumTNG team, the study's lead author, suggests that these results may help resolve discrepancies between the matter clustering inferred from weak lensing and the cosmic microwave background. Another exciting finding pertains to the recent discovery of a group of highly massive galaxies in the early universe by the James Webb Space Telescope. Dr. Rahul Kannan confirmed that the new results from the JWST could conflict with the predictions of the simulation, hinting at the possibility of more efficient star formation shortly after the Big Bang.

Aside from these initial studies, the MillenniumTNG project also lends a hand in devising strategies to analyze upcoming cosmological data. As Prof. Volker Springel from MPA, the project's principal investigator, points out, "MillenniumTNG combines recent advances in simulating galaxy formation with the field of cosmic large-scale structure, allowing an improved theoretical modeling of the connection of galaxies to the dark matter backbone of the Universe." Over 3 Petabytes of simulation data generated by the project will be a treasure trove for future investigations, promising to keep scientists engrossed for years to come.