So far, no dark matter candidates have been detected.

Dark matter, as previous Picture of the Day articles report, is undetectable, except through its supposed gravitational interactions with luminous, or baryonic matter. Large, expensive experiments are currently investigating many aspects of its hidden qualities, including a search for the particle (or particles) that comprises its substance.

One such experiment is the Axion Dark Matter Experiment (ADMX). Axions are theoretical particles that are thought to be responsible for breaking what quantum physics describes as “charge-parity symmetry“. It is not the point of this article to delve into the morass of assumptions that makes up quantum mechanics. Suffice to say, axions are one of the contenders in the search for dark matter particles.

It was once thought that “cold, non-radiating matter”, such as burned-out stars, or large planets exert forces on galactic structures. These “normal” but invisible structures were called MAssive Compact Halo Objects (MACHOs). Telescopes looked for stellar occultations caused by MACHOs. However, years of investigation returned no discoveries. This led researchers to acknowledge that MACHOs are not dark matter candidates...........