How Zwicky already ruled out modified gravity theories without dark matter

TL;DR

This paper examines modified gravity theories as alternatives to dark matter, demonstrating their failure to explain galaxy cluster observations like A1689, and confirms the necessity of dark matter, as originally argued by Zwicky.

Contribution

It critically tests modified gravity theories against galaxy cluster data, reaffirming the need for dark matter and highlighting Zwicky's original argument against modified gravity.

Findings

Modified gravity theories fail to explain galaxy cluster lensing and X-ray data.

Dark matter, possibly neutrinos, remains necessary to account for observations.

Zwicky's original argument against modified gravity is supported by current data.

Abstract

Various theories, such as MOND, MOG, Emergent Gravity and $f(R)$ theories avoid dark matter by assuming a change in General Relativity and/or in Newton's law. Galactic rotation curves are typically described well. Here the application to galaxy clusters is considered, focussed on the good lensing and X-ray data for A1689. As a start, the no-dark-matter case is confirmed to work badly: the need for dark matter starts near the cluster centre, where Newton's law is still supposed to be valid. This leads to the conundrum discovered by Zwicky, which is likely only solvable in his way, namely by assuming additional (dark) matter. Neutrinos with eV masses serve well without altering the successes in (dwarf) galaxies.