A possible tension between galaxy rotational velocity and observed physical properties

TL;DR

This study reveals a significant brightness difference between galaxies spinning in the same or opposite direction to the Milky Way, suggesting a potential tension with existing galaxy rotation theories and indicating possible new physics or large-scale structure effects.

Contribution

It presents novel observational evidence of brightness asymmetry related to galaxy spin direction, challenging current understanding of galaxy rotation and large-scale cosmic structure.

Findings

Brightness differences correlate with galaxy spin direction.

Differences are consistent across multiple instruments and methods.

Potential implications for parity violation and cosmological tensions.

Abstract

The discrepancy between the mass of galaxies and their rotational velocity is one of the most puzzling scientific phenomena. Despite over a century of research, this phenomenon is not fully understood. Common explanations include dark matter and MOND, among other theories. Here we report on another observation that shows tension between the physics of galaxy rotation and its rotational velocity. We compare the brightness of galaxies, and find that galaxies that spin in the same direction as the Milky Way have different brightness than galaxies that spin in the opposite direction. While such difference in brightness is expected due to Doppler shift, it is expected to be subtle. The results show that the difference in brightness is large enough to be detected by Earth-based telescopes. That observed difference corresponds to physical properties of galaxies with far greater rotational velocity than the rotational velocity of the Milky Way. The difference is consistent in both the Northern galactic pole and the Southern galactic pole, and is not observed in parts of the sky that are perpendicular to the galactic pole. The differences are observed by several different instruments such DECam, SDSS, Pan-STARRS, and HST. The observation is also consistent across annotation methods, including different computer-based methods, manual annotation, or crowdsourcing annotations through Galaxy Zoo, all show similar results. Another possible explanation to the observation is parity violation in the large-scale structure, such that the magnitude of the parity violation was stronger in the earlier Universe. It can also be linked to other anomalies such as the Ho tension. Analysis of Ho using Ia supernovae shows smaller Ho tension when the spin directions of the host galaxies are consistent, although these results are based on a small number of supernovae, and may not be statistically significant.