Hydrogen gas became trapped in puddles of the invisible material and began spinning rapidly in dark matter's gravitational whirlpool, forming stars at a furious rate.

A nearly invisible material like fishing line can be used to sew each knot of net to the fabric (often with a drop of glue for strength).

Until then it was difficult to decide the status of these invisible materials.

They could not determine what the invisible material of the bow consisted of.

The way stars clump, the velocity at which galaxies spin and the behavior of huge gas clouds all suggest the presence of gravitational forces produced by invisible material.

Mr. Barry credits his father with his fascination for invisible materials.

They identified clumps of dark matter stretching between galaxies over more than a billion light years, providing the first picture of the invisible material on such a large scale.

As much as 99 percent of the universe is believed to consist of "dark matter," invisible material whose composition is unknown.

Ben Miller looks at dark matter, the strange invisible material that fills the universe.

They learn that Fellpool blood could be used to process a special, invisible material which could give them a massive advantage in the war.