A screenshot from Firefly, an interactive, web-based, and publicly available particle visualization platform created by Aaron Geller and Alex Gurvich. Shown here is a snapshot in time from a simulation of a Milky Way-like galaxy with the stars in blue, the gas in red, and the dark matter in yellow. In the real universe the gas and dark matter is invisible, so we use computer simulations like the one visualized here to understand how the light we see from galaxies is related to these invisible components.
Credit: Aaron Geller / Alex Gurvich / Northwestern