Distinct radial acceleration relations of galaxies and galaxy clusters supports hyperconical modified gravity

TL;DR

This paper investigates a relativistic hyperconical gravity model that explains galaxy and galaxy cluster dynamics without dark matter, fitting observational data with minimal parameters and supporting modified gravity theories.

Contribution

It introduces a hyperconical relativistic gravity model that fits galaxy and cluster radial acceleration relations with few parameters, advancing modified gravity theories.

Findings

The hyperconical model fits most galaxy cluster and galaxy rotation data.

A simple relation with one or two parameters suffices for most observations.

The model shows acceptable statistical fit metrics, supporting its viability.

Abstract

General relativity (GR) is the most successful theory of gravity, with great observational support on local scales. However, to keep GR valid over cosmic scales, some phenomena (such as flat galaxy rotation curves and the cosmic expansion history) require the assumption of exotic dark matter. The radial acceleration relation (RAR) indicates a tight correlation between dynamical mass and baryonic mass in galaxies. This suggests that the observations could be better explained by modified gravity theories without exotic matter. Modified Newtonian Dynamics (MOND) is an alternative theory that was originally designed to explain flat galaxy rotation curves by using a new fundamental constant acceleration $a_0$, the so-called Milgromian parameter. However, this non-relativistic model is too rigid (with insufficient parameters) to fit the large diversity of observational phenomena. In contrast, a relativistic MOND-like gravity naturally emerges from the hyperconical model, which derives a fictitious acceleration compatible with observations. This study analyses the compatibility of the hyperconical model with respect to distinct RAR observations of 10 galaxy clusters obtained from HIFLUGCS and 60 high-quality SPARC galaxy rotation curves. The results show that a general relation can be fitted to most cases with only one or two parameters, with an acceptable $\chi^2$ and $p$-value. These findings suggest a possible way to complete the proposed modification of GR on cosmic scales.