The Empirical Laws of Galaxy Dynamics: Challenges to the Standard Model and Support for MOND

Core Concepts

This review paper argues that observed empirical laws of galaxy dynamics, particularly at large radii as revealed by weak gravitational lensing, pose significant challenges to the standard Lambda Cold Dark Matter (ΛCDM) model while aligning remarkably well with predictions made by Modified Newtonian Dynamics (MOND).

Abstract

• Bibliographic Information: Lelli, F., Mistele, T., McGaugh, S.S., Schombert, J.M., & Li, P. (2024). The empirical laws of galaxy dynamics: from gas kinematics to weak lensing. In D.M. Worrall (Ed.), Astronomy in Focus, Focus Meeting 9, XXXIInd IAU General Assembly, August 2024 ( [DOI: 00.0000/X000000000000000X](DOI: 00.0000/X000000000000000X)). International Astronomical Union.

• Research Objective: This review paper examines recent findings in galaxy dynamics, particularly from weak gravitational lensing studies, to assess their consistency with the predictions of both the standard ΛCDM model and MOND.

• Methodology: The authors review empirical laws of galaxy dynamics, including flat rotation curves, the Baryonic Tully-Fisher Relation (BTFR), and the Radial Acceleration Relation (RAR). They focus on recent weak lensing data, which allows for the study of galaxy dynamics at larger radii than previously possible. The authors compare these observations with the predictions of both ΛCDM and MOND.

• Key Findings: Weak lensing data reveals that the rotation curves of both late-type and early-type galaxies remain flat out to several hundreds of kiloparsecs, well beyond the virial radius expected in ΛCDM. This observation supports the existence of a fundamental acceleration scale, a key tenet of MOND. Additionally, both kinematic and weak lensing data show that late-type and early-type galaxies follow the same BTFR and RAR, further strengthening the case for MOND.

• Main Conclusions: The authors conclude that the empirical laws of galaxy dynamics, particularly the flatness of rotation curves at large radii, pose significant challenges to the standard ΛCDM model. They argue that these observations are naturally explained by MOND, which predicted many of these relationships before they were observed.

• Significance: This review highlights the discrepancies between observations of galaxy dynamics and the predictions of the standard ΛCDM model. The authors argue that these discrepancies challenge the prevailing understanding of dark matter and galaxy formation. The remarkable agreement between observations and MOND predictions suggests that alternative theories of gravity, such as MOND, may provide a more accurate description of gravity on galactic scales.

• Limitations and Future Research: The authors acknowledge the limitations of weak lensing observations, particularly the need for extrapolation at large radii. Future research with higher-resolution and deeper lensing surveys will be crucial to confirm these findings and further test the predictions of both ΛCDM and MOND.

Stats

The radial acceleration relation (RAR) covers about 16 orders of magnitude in the Newtonian baryonic acceleration, combining galaxy data with Solar System data.
The characteristic acceleration scale where the observed acceleration deviates from the Newtonian baryonic acceleration is ~10^-10 m s^-2.
Weak lensing data allows studying galaxy dynamics out to several hundreds of kpc, extending beyond the virial radius of their expected dark matter halos.

Quotes

"Remarkably, these empirical facts were predicted a priori by MOND."
"In the ΛCDM context, each one of the dynamical laws implies a different type of baryon-DM coupling and/or fine-tuning problem in galaxy formation."
"The empirical laws of galaxy dynamics have been mostly studied in late-type galaxies (LTGs; spirals and dwarf irregulars) because they usually possess a rotation-supported gas disk with negligible pressure support, so that the circular velocity is directly probed by the observed rotation speeds."

Key Insights Distilled From

The empirical laws of galaxy dynamics: from gas kinematics to weak lensing

by Federico Lel... at arxiv.org 11-06-2024

https://arxiv.org/pdf/2411.02499.pdf