Cosmic filaments could reveal dark matter type, but telescopes can't resolve the details.

Most matter in the universe sits in a giant web of cosmic filaments. Dark matterDark matterInvisible matter that does not emit light but affects the universe through gravity. shapes these filaments. Cold dark matter creates small clumps, while warm dark matter smooths them out. Scientists wanted to test if radio signals from hydrogen gas, called 21cm emission21cm emissionRadio waves from neutral hydrogen gas, used to map cosmic structures., could tell these two dark matter types apart. To find out, researchers used computer simulations of the universe at redshifts z=4 and 2.5 to map this gas emission. They blurred these maps with simulated telescope beams to mimic real radio telescopes, specifically SKA1-Low and the planned SKA2-Low. They found that real filaments look noticeably different between the two dark matter models, especially at z=4. However, smoothing maps with telescope beams quickly erases these tiny differences, especially for beams larger than 6 arcsec. Consequently, neither telescope can resolve individual filaments well enough to tell the dark matter models apart.

Why it matters

This matters for astronomers trying to understand what dark matter is, as one method to tell models apart appears limited. If we can't see the filament details, we need other ways to probe dark matter's nature.

Questions answered