Dark matter is a type of matter hypothesized to account
for a large part of the total mass in the universe.
Dark matter cannot be seen directly with telescopes;
evidently it neither emits nor absorbs light or other
electromagnetic radiation at any significant level.
Instead, its existence and properties are inferred from
its gravitational effects on visible matter, radiation,
and the large scale structure of the universe.
Dark matter is estimated to constitute 84%%
of the matter in the universe and 23%% of the mass-energy.