The Radial Acceleration Relation in Rotationally Supported Galaxies (1609.05917v1)

Abstract: We report a correlation between the radial acceleration traced by rotation curves and that predicted by the observed distribution of baryons. The same relation is followed by 2693 points in 153 galaxies with very different morphologies, masses, sizes, and gas fractions. The correlation persists even when dark matter dominates. Consequently, the dark matter contribution is fully specified by that of the baryons. The observed scatter is small and largely dominated by observational uncertainties. This radial acceleration relation is tantamount to a natural law for rotating galaxies.

• The paper establishes that the observed radial acceleration in 153 galaxies consistently correlates with baryonic predictions, suggesting a fundamental galactic law.
• Using near-infrared SPARC photometry and detailed rotation curves, the study derives an empirical formula with a single acceleration scale, g0, and minimal scatter.
• The findings challenge standard dark matter frameworks by implying a direct link between baryonic matter and galaxy dynamics, prompting revised formation models.

An Analysis of the Radial Acceleration Relation in Rotationally Supported Galaxies

In the paper titled The Radial Acceleration Relation in Rotationally Supported Galaxies, the authors present a detailed investigation into the relationship between the radial acceleration traced by the rotation curves of galaxies and the acceleration predicted by the baryonic matter's distribution. Spanning an extensive sample of 2693 data points from 153 galaxies of varying morphological characteristics, the authors identify a significant correlation that they term as the radial acceleration relation (RAR).

Key Findings

The paper ingeniously utilizes near-infrared photometry data from the SPARC (Spitzer Photometry and Accurate Rotation Curves) database to delineate the mass distribution of baryons. These are compared against the dynamics obtained from rotational velocity measurements. A salient feature of the paper is the consistent correlation observed across a class of galaxies ranging from high to low mass and surface brightness. Significantly, this relationship holds irrespective of the presence of dark matter, suggesting that the apparent dark matter distribution is inherently linked to the baryonic matter.

The authors propose an empirical fit to the data, described by: $$g_{\text{obs}} = \frac{g_{\text{bar}}}{1 - e^{-\sqrt{g_{\text{bar}}/g_0}}},$$ where $g_{\text{obs}}$ is the observed acceleration, $g_{\text{bar}}$ is the baryonic acceleration, and $g_0$ is the only fit parameter, an acceleration scale. The minimal scatter about this relation underscores its potential as a natural law governing galaxy dynamics.

Theoretical Implications and Discussion

The robustness and small scatter of the RAR provoke a theoretical reevaluation of dark matter and galactic dynamics:

1. Galaxy Formation Models: The data confronts traditional cold dark matter (CDM) models, which typically require complex feedback mechanisms to replicate observed galaxy properties. The RAR suggests a simpler regulatory mechanism linking baryonic content to galactic dynamics, challenging simulation efforts to incorporate this empirical relationship naturally.
2. Dark Sector Physics: Alternatively, the RAR might imply a restricted interaction within the dark sector itself or between dark matter and baryons. The gravitational framework might need modification to account for this coupling, potentially in terms of dark fluid models or theories allowing gravitational polarization.
3. Quantum of Dynamics: RAR intriguingly aligns with Modified Newtonian Dynamics (MOND), a framework where traditional gravitational dynamics are altered at low accelerations. While MOND has faced skepticism, the empirical grounding provided by the RAR invites renewed analysis, particularly to discern its utility against dark matter paradigms.

Future Directions

The implications of RAR are profound, pressing both observations and theoretical physics towards understanding its universality across different galactic systems. Further research is necessary to refine the observational techniques, particularly in assessing the methods and accuracy of measuring galaxy inclinations and distances, which bear on the calculated rotational velocities. Theoretical advancements may focus on integrating the RAR within cosmological models, exploring astrophysical mechanisms that preserve its integrity. Additionally, any bridge extended between RAR and small-scale structure formation, like dwarfs and elliptical galaxies, could significantly alter our cosmic data interpretation and modeling techniques.

Conclusion

The radial acceleration relation is a compelling empirical observation that challenges the preconceived interplay between baryonic matter and dark matter in galaxies. Whether it steers future discoveries within known paradigms or necessitates new physics remains an exciting open question for astronomers and physicists alike. The research delineated in this paper advances a critical discourse on the true nature of galactic structure, dynamics, and the underlying laws governing them.