NASA's Astronomy Picture of the Day (APOD) for 25 October 2026 features a visualization titled "Dark Matter in a Simulated Universe." Selected by the site's team as the astronomy image of the day, it offers a visual representation of how dark matter is distributed on large scales within a computer-reconstructed universe, rather than a direct observation of the cosmos.

APOD is an outreach service run by NASA and Michigan Technological University that publishes a daily image or photograph of the universe accompanied by a short explanation written by a professional astronomer. In this case, the caption focuses on dark matter, the invisible component that makes up most of the mass of the universe and whose nature remains one of the major open problems in astrophysics.

Cosmological simulations are precisely one of the key tools for studying it: by feeding the initial conditions of the early universe and the laws of gravitation into a computer model, the formation of the cosmic web of filaments and halos hosting dark matter is reproduced and the result compared with observations of galaxies and gravitational lensing.

The full image, together with the detailed scientific explanation that accompanies it, can be found on the APOD page for 25 October 2026.