The astronomers used gravitational lensing to detect the dark matter filaments.
[7] The cluster is connected by a filament of dark matter to Abell 223 that is permeated by hot X-ray emitting gas.
Astronomers have not been able to locate the full 5% of baryonic matter within other galaxies, stars or gases.
This was difficult to locate because the gas had a very low density, which made it hard to detect.
It is within Earth's line of sight, so scientists were able to see a strong concentration of this extremely distant gas with the latest high-power infrared and X-ray telescopes, within a section of the sky.