Question

what is dark matter?

Answer 1

nonluminous material that is postulated to exist in space and that could take any of several forms including weakly interacting particles ( cold dark matter ) or high-energy randomly moving particles created soon after the Big Bang

Answer 2

Dark matter is a hypothetical form of matterthat is thought to account for approximately 85% of the matter in the universe, and about a quarter of its total energy density. The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles.