Galactic dance reveals that the universe is smaller than thought

Galaxies are located in a massive galaxy group. Upon entering the cluster, these galaxies show a blueshift compared to the central galaxy. Credit: Dr. Shihong Liao

A study using Sloan Digital Sky Survey data has revealed that the universe may be younger than expected, challenging traditional cosmological models by analyzing the motions of space galaxies around massive clusters.

In standard cosmological models, the formation of cosmological structures begins with the emergence of small structures, which subsequently undergo hierarchical merging, leading to the formation of larger systems. As the universe ages, massive galaxy groups and clusters, as the largest systems, tend to increase in mass and reach a more dynamically relaxed state.

The motions of space galaxies around these groups and clusters provide valuable insights into their assembly state. Observations of such motion provide important clues about the age of the universe.

Using public data from the Sloan Digital Sky Survey (SDSS), a research team led by Professor Qi Guo of the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) analyzed the kinematics of satellite pairs around massive galaxy clusters. The team's findings suggest that the universe may be younger than predicted by the LCDM model with cosmological Planck parameters.

This study was published in Nature astronomy On January 22nd.

Cumulative fraction of bonded pairs as a function of tolerance angle

Cumulative fraction of bonded pairs as a function of tolerance angle. Credit: Dr. Cheng Guo

The researchers investigated the motion of pairs of satellites positioned on the far side of massive galaxy clusters using their velocity offsets from the central galaxy along the line of sight. They found a significant excess of pairs showing correlated velocity shifts compared to pairs showing anticorrelated velocity shifts.

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“The increase in correlated satellite pairs indicates the presence of recently accreted or fallen space galaxies,” said Professor Qi Guo, corresponding author of the paper.

This excess was also found in modern cosmological simulations, but the magnitude of this effect was much smaller than in observations. The large discrepancy between observations and simulations indicates that massive galaxy clusters are younger in the real universe.

“Since the age of massive galaxy clusters can be closely related to the age of the Universe, these results therefore suggest a younger Universe compared to that derived from the cosmic microwave background (CMB) by the Planck Collaboration,” said Dr. Qing Guo. , first author of the paper.

These results represent a challenge to the current cosmological model and may provide valuable insights into the Hubble tensor problem.

Reference: “Younger Universe Indicated by Satellite Pair Correlations from SDSS Observations of Massive Galaxy Clusters” by Qing Guo, Qi Guo, Marius Cotton, Shi Shao, Wenxiang Pei, Wenting Wang, Liang Gao, and Jie Wang, 22 January 2024, Nature astronomy.
doi: 10.1038/s41550-023-02192-6

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