An excess of small-scale gravitational lenses observed in galaxy clusters

TL;DR

This study compares observed gravitational lensing in galaxy clusters with CDM simulation predictions, finding significantly more efficient lensing by substructures than expected, suggesting potential issues with current models or assumptions.

Contribution

It introduces a new metric for analyzing dark matter substructures in clusters and reveals a discrepancy between observations and CDM simulations.

Findings

Observed substructures are over ten times more efficient lenses than simulations predict.

The discrepancy may indicate systematic issues in simulations or incorrect dark matter assumptions.

Results challenge current understanding of dark matter distribution in galaxy clusters.

Abstract

Cold dark matter (CDM) constitutes most of the matter in the Universe. The interplay between dark and luminous matter in dense cosmic environments like galaxy clusters is studied theoretically using cosmological simulations. Observed gravitational lensing is used to test and characterize the properties of substructures - the small-scale distribution of dark matter - in clusters. An apt metric, the probability of strong lensing events produced by dark matter substructure, is devised and computed for 11 galaxy clusters. We report that observed cluster substructures are more efficient lenses than predicted by CDM simulations, by more than an order of magnitude. We suggest that hitherto undiagnosed systematic issues with simulations or incorrect assumptions about the properties of dark matter could explain our results.