DARK MATTER: A HELD-OUT TOPIC
Dark matter is inferred from gravitational effects. Visible matter alone does not explain several observations of galaxies and clusters under the usual models. Astronomers also study gravitational lensing, where the paths of light reveal the influence of mass.

The name does not identify a confirmed particle. Evidence for an unseen gravitational component and certainty about its microscopic nature are different claims. The first has observational support; the second remains unresolved.

An explanation should identify what was observed and what was inferred. A proposed dark-matter candidate requires tests and evidence. Calling a candidate established would overstate current knowledge. There is no justification for claiming a universal answer just because a model can generate fluent text.

Source for the physical claims: https://science.nasa.gov/missions/hubble/dark-matter/
The distinction between answer confidence and evidence is project-authored guidance.