These hypothetical particles are known as cold dark matter because they move so slowly.

Diesel fuel produces more potentially hazardous pollution, known as particulate matter, than natural gas.

Of particular concern is a class of particles known as fine particulate matter or PM2.5 that gets deep into the lung.

The dark parts are known as grey matter and the lighter parts as white matter.

Zwicky hypothesised that there must be a great deal of non-luminous matter in the galaxy clusters, which became known as dark matter.

Material not so excluded is known as patentable subject matter.

The missing component is known as dark matter and its nature is unknown.

This exotic form of matter is known as degenerate matter.

A widely supported theory, of hypothetical invisible particles known as cold dark matter, was dealt a serious blow this year.

Scientists believe that huge clumps of the stuff are spread throughout space where their gravitational fields attract what we know as normal matter.