PRESS ASSOCIATION -- A gem of a world made from diamond has been discovered orbiting a tiny spinning star 4,000 light years away.

The "diamond planet" is actually the shrunken core of a once massive star.

Despite being only five times the size of the Earth, it has more mass than Jupiter.

Its high density shows that it must largely be made of crystalline carbon - in other words, diamond.

"This remnant is likely to be largely carbon and oxygen, because a star made of lighter elements like hydrogen and helium would be too big to fit the measured orbiting times," said Dr Michael Keith, from the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO).

The spinning star, around the size of a small city, is known as a "pulsar".

As the star spins more than 10,000 times a minute it acts like a lighthouse, sending out a beam of radio waves that sweeps repeatedly over the Earth.

Patterns in the pulses caused by gravitational pull provide key information about the star's companion.

The discovery was reported in the journal Science.