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A direct empirical proof of the existence of dark matter

Douglas Clowe, Marusa Bradac, Anthony H. Gonzalez, Maxim Markevitch, Scott W. Randall, Christine Jones, Dennis Zaritsky

TL;DR

The paper presents a direct empirical test for dark matter using a major cluster merger, exploiting a spatial separation between collisionless galaxies and the X-ray–visible plasma. By constructing a high-significance κ map from deep, multi-instrument weak-lensing data, the study shows mass peaks tracing galaxies rather than the dominant baryonic plasma, at 8σ–12σ significance. The results argue that most cluster mass is unseen and does not follow the plasma, providing strong, gravity-law–independent evidence for dark matter and challenging modified gravity scenarios relying on baryons alone. The work also strengthens confidence in the collisionless nature of dark matter and complements similar findings in other merging clusters.

Abstract

We present new weak lensing observations of 1E0657-558 (z=0.296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray emitting plasma are spatially segregated. By using both wide-field ground based images and HST/ACS images of the cluster cores, we create gravitational lensing maps which show that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8-sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen.

A direct empirical proof of the existence of dark matter

TL;DR

The paper presents a direct empirical test for dark matter using a major cluster merger, exploiting a spatial separation between collisionless galaxies and the X-ray–visible plasma. By constructing a high-significance κ map from deep, multi-instrument weak-lensing data, the study shows mass peaks tracing galaxies rather than the dominant baryonic plasma, at 8σ–12σ significance. The results argue that most cluster mass is unseen and does not follow the plasma, providing strong, gravity-law–independent evidence for dark matter and challenging modified gravity scenarios relying on baryons alone. The work also strengthens confidence in the collisionless nature of dark matter and complements similar findings in other merging clusters.

Abstract

We present new weak lensing observations of 1E0657-558 (z=0.296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray emitting plasma are spatially segregated. By using both wide-field ground based images and HST/ACS images of the cluster cores, we create gravitational lensing maps which show that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8-sigma significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law, and thus proves that the majority of the matter in the system is unseen.

Paper Structure

This paper contains 4 sections, 1 equation, 1 figure.

Table of Contents

  1. Introduction
  2. Methodology and Data
  3. Analysis
  4. Discussion

Figures (1)

  • Figure 1: Shown above in the top panel is a color image from the Magellan images of the merging cluster 1E0657$-$558, with the white bar indicating 200 kpc at the distance of the cluster. In the bottom panel is a 500 ks Chandra image of the cluster. Shown in green contours in both panels are the weak lensing $\kappa$ reconstruction with the outer contour level at $\kappa =$ 0.16 and increasing in steps of 0.07. The white contours show the errors on the positions of the $\kappa$ peaks and correspond to $68.3\%$, $95.5\%$, and $99.7\%$ confidence levels. The blue $+$s show the location of the centers used to measure the masses of the plasma clouds in Table \ref{['table2']}.