Younger Universe Suggested by Galaxy Group Study

A new study published in Nature Astronomy suggests that the universe may be younger than predicted by the standard cosmological models. The study analyzed the motions of satellite pairs around massive galaxy groups, which provide clues about the age and formation of these structures.

What are satellite pairs?

Satellite pairs are galaxies that orbit around a massive galaxy group or cluster. They are positioned on the opposite side of the group or cluster from each other, and they have different velocity offsets from the central galaxy along the line of sight. Velocity offset is the difference between the speed of a galaxy and the speed of the central galaxy.

What did the study find?

The study used public data from the Sloan Digital Sky Survey (SDSS) to investigate the movement of satellite pairs around massive galaxy groups. The researchers discovered a notable excess of pairs exhibiting correlated velocity offsets compared to pairs displaying anti-correlated velocity offsets.

This means that more satellite pairs are moving in the same direction as the central galaxy than moving in the opposite direction. This suggests that these satellite pairs are recently accreted or infalling, meaning that they have joined the group or cluster recently.

What does this imply?

The excess of correlated satellite pairs indicates that massive galaxy groups are younger in the real universe than in cosmological simulations. The simulations are based on the standard cosmological model, which assumes that small structures merge to form larger ones over time. As the universe ages, massive galaxy groups and clusters are expected to reach a more dynamically relaxed state, where satellite pairs have more balanced velocity offsets.

However, the observations show that massive galaxy groups are still in a more active state, where satellite pairs are still being captured or falling into them. This implies that these structures have not had enough time to reach equilibrium, and thus the universe is younger than predicted by the model.

The study estimates that the universe may be about 1 billion years younger than derived from the cosmic microwave background (CMB) by the Planck Collaboration. The CMB is the oldest light in the universe, and it reflects the conditions of the early universe. The Planck Collaboration is a project that measures the CMB with high precision.

Why is this important?

The findings of this study challenge the current cosmological model and may provide valuable insights into the Hubble tension problem. The Hubble tension is a discrepancy between two different methods of measuring the expansion rate of the universe, known as the Hubble constant. One method uses CMB data and cosmological simulations, while another method uses observations of distant supernovae and other objects.

The two methods produce different values for the Hubble constant, which implies that either one of them is wrong, or there is something missing in our understanding of the universe. The study suggests that using a younger age for the universe may help resolve this tension, as it would imply a higher expansion rate.