# A lensed radio jet at milli-arcsecond resolution II: Constraints on fuzzy dark matter from an extended gravitational arc

**Authors:** Devon M. Powell, Simona Vegetti, J. P. McKean, Simon D. M. White, Elisa G. M. Ferreira, Simon May, Cristiana Spingola  
**arXiv:** [2302.10941](https://arxiv.org/abs/2302.10941)  
**Date:** 2023-02-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2302.10941v1/

## Key points

- Researchers used very long baseline interferometry (VLBI) to observe a gravitational lens system at an impressive resolution of less than 5 milli-arcseconds.
- The aim of the study was to investigate the properties of fuzzy dark matter (FDM) particles.
- FDM particles with masses below $4.4\times10^{-21}~\mathrm{eV}$ are ruled out with a high confidence level.
- The research extends its findings to non-scalar and multiple-field models such as vector FDM, excluding FDM particles with masses greater than $1.4 \times 10^{-21}~\mathrm{eV}$ based on their analysis.
- The observation takes into account the extended source structure and high angular resolution, allowing for direct sensitivity to granule structures in the main dark matter halo of the lens system.
- Comparing with previous analyses, this study's lower bounds on FDM particle mass are competitive and provide valuable insights into dark matter physics.
- Future observations conducted at higher resolutions have the potential to further improve constraints on FDM particle masses by up to two orders of magnitude.

## Summary

In a recent study, researchers used very long baseline interferometry (VLBI) to observe a single gravitational lens system at an impressive resolution of less than 5 milli-arcseconds. The aim of the study was to investigate the properties of fuzzy dark matter (FDM) particles. By analyzing the data, the researchers were able to place a lower limit on the mass of the FDM particle. They found that FDM particles with masses below $4.4\times10^{-21}~\mathrm{eV}$ are ruled out with a high confidence level, as indicated by a 20:1 posterior odds ratio relative to a smooth lens model. This result provides important constraints on the nature of dark matter and contributes to our understanding of its fundamental properties. Furthermore, this research extends its findings to non-scalar and multiple-field models such as vector FDM. In these scenarios they establish that FDM particles with masses greater than $1.4 \times 10^{-21}~\mathrm{eV}$ are excluded based on their analysis. One notable aspect of this research is that it takes into account the extended source structure and high angular resolution of the observation which allows for direct sensitivity to granule structures present in the main dark matter halo of the lens system. These granule structures are considered a generic prediction of FDM theories and their robustness is supported by a model based on well-understood physics related to ultra-light dark matter fields in a gravitational potential well. This ensures that their findings remain valid across a wide range of assumed dark matter fractions and velocity dispersions within the lens galaxy. Comparing their results with previous analyses which often rely on intermediate modeling techniques or consider baryonic effects, this study's lower bounds on FDM particle mass are competitive and provide valuable insights into dark matter physics. Looking ahead, future observations conducted at higher resolutions between 10 and 100 GHz have the potential to further improve constraints on FDM particle masses by up to two orders of magnitude; highlighting the importance of continued advancements in observational techniques for unraveling mysteries surrounding dark matter.