NASA | MSFC | SAO | Chandra X-ray Observatory | 2020 Mar 19
press release, researchers used Chandra to look for signs of an as-yet undetected particle predicted by string theory. The lack of a detection in these Chandra observations helps rule out some versions of string theory.
The team looked for extraordinarily low-mass "axion-like" particles in the Perseus galaxy cluster, shown in a Chandra image in the main panel of this graphic (red, green and blue colors are low, medium and high X-ray energies respectively). Galaxy clusters, the largest structures in the Universe held together by gravity, offer an excellent opportunity to search for these particles. In a galaxy cluster, X-ray photons from an embedded or a background source can travel through a large amount of hot gas permeated with magnetic field lines. Some of the X-ray photons may undergo conversion into axion-like particles, or the other way around, along this journey.
A simplified illustration shows this process, with shorter wavelength X-ray photons (in blue) converting into axion-like particles (yellow) and back to photons, as they travel across magnetic field lines (grey) in the cluster. Longer wavelength X-ray photons (red) are converting into axion-like particles, but not back into photons. Such conversions would cause a distortion in the X-ray spectrum (the amount of X-rays at different energies) of a bright or embedded source of X-rays. ...
Astrophysical Limits on Very Light Axion-like Particles
from Chandra Grating Spectroscopy of NGC 1275 ~ Christopher S. Reynolds et al