Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions

Area of Science:

• Astrophysics
• Cosmology
• Theoretical Physics

Background:

• Astronomical data consistently show mass discrepancies in extragalactic systems, where observed motions exceed predictions based on visible matter.
• Current interpretations include the existence of dark matter or a fundamental breakdown in our understanding of gravitational dynamics.
• Outstanding observational challenges exist for the standard dark matter paradigm in explaining galactic mass discrepancies.

Purpose of the Study:

• To review observational challenges for the dark matter interpretation of galactic mass discrepancies.
• To investigate Milgrom's law and its potential as an alternative explanation for these discrepancies.
• To assess the successes and problems of Modified Newtonian Dynamics (MOND) across astrophysical scales and review theoretical frameworks.

Main Methods:

• Review of observational data and existing challenges for dark matter in galaxies.
• Analysis of Milgrom's law, relating galactic dynamics to a fundamental acceleration constant (a₀).
• Comprehensive review of observational evidence for and against MOND, and theoretical relativistic extensions (e.g., TeVeS, GEA, BIMOND).

Main Results:

• Several puzzling galactic observations are predicted by Milgrom's law, suggesting a modification of Newtonian dynamics (MOND) on galactic scales.
• MOND provides a potential explanation for mass discrepancies without invoking unseen matter.
• The study summarizes the current state of MOND, including its observational successes, persistent problems, and theoretical developments.

Conclusions:

• Milgrom's law and MOND present a compelling alternative to dark matter for explaining galactic dynamics.
• Further theoretical and observational work is needed to fully embed MOND within a relativistic framework and address remaining challenges.
• The findings suggest a potential revision of gravitational laws on large scales.