Einstein rings modulated by wavelike dark matter from anomalies in gravitationally lensed images

Unveiling the true nature of dark matter, which manifests itself only through gravity, is one of the principal quests in physics. Leading candidates for dark matter are weakly interacting massive particles or ultralight bosons (axions), at opposite extremes in mass scales, that have been postulated by competing theories to solve deficiencies in the Standard Model of particle physics. Whereas dark matter weakly interacting massive particles behave like discrete particles (rho DM), quantum interference between dark matter axions is manifested as waves (psi DM). Here, we show that gravitational lensing leaves signatures in multiply lensed images of background galaxies that reveal whether the foreground lensing galaxy inhabits a rho DM or psi DM halo. Whereas rho DM lens models leave well documented anomalies between the predicted and observed brightnesses and positions of multiply lensed images, psi DM lens models correctly predict the level of anomalies remaining with rho DM lens models. More challengingly, when subjected to a battery of tests for reproducing the quadruply lensed triplet images in the system HS 0810+2554, psi DM is able to reproduce all aspects of this system whereas rho DM often fails. The ability of psi DM to resolve lensing anomalies even in demanding cases such as HS 0810+2554, together with its success in reproducing other astrophysical observations, tilt the balance toward new physics invoking axions. Modelling of the gravitationally lensed system HS 0810+2554 with wavelike dark matter resolves brightness and position anomalies remaining after the standard massive-particle dark matter treatment.

Automated summary

Unveiling the true nature of dark matter, which only interacts gravitationally, is a major goal in physics. Weakly interacting massive particles and ultralight bosons (axions) are leading candidates for dark matter, postulated to address deficiencies in the Standard Model of particle physics. By examining the lensing signatures in multiply lensed images of background galaxies, researchers can distinguish between rho DM and psi DM halos, with rho DM models showing discrepancies in brightness and position predictions. In the case of the system HS 0810+2554, psi DM successfully reproduces all aspects of the lensed triplet images, while rho DM often fails. This, combined with its ability to resolve lensing anomalies, supports the idea of wavelike dark matter involving axions.