Scientists have been able to observe the universe and determine that about 80% of the its mass appears to be “dark matter,” which exerts a gravitational pull but does not interact with light, and thus can’t be seen with telescopes. Our current understanding of cosmology and nuclear physics suggests that dark matter could be made of axions, hypothetical particles with unusual symmetry properties.
Source:
https://phys.org/news/2020-05-dark-universe-coldest-material.html