Astronomers from the University of Manchester and other international colleagues have discovered a rare planet that seems to be made of diamond.

In a study published in the Science journal the research team, led by Professor Matthew Bailes of Swinburne University of Technology in Australia, concluded that the new planet racing around a pulsar is largely made up of carbon. The planet is so dense that scientists calculate that the core must be made up of carbon and oxygen and is crystallized.

"The evolutionary history and amazing density of the planet all suggest it is comprised of carbon -- i.e. a massive diamond orbiting a neutron star every two hours in an orbit so tight it would fit inside our own Sun," said Professor Bailes.

The unusual planet was discovered as scientists were observing the pulsar- a tiny dead neutron star that spins around hundreds of times a second and emits beams of radiation. Irregular movements in the beams clued scientists in that there was a companion planet orbiting the pulsar.

The planet which lies 4,000 light years from Earth, measures up to 60,000km across about five times the Earth's diameter and is about 300 times heavier. It is believed to be the remnant of a once massive star that lost its outer layers to the pulsar star it orbits leaving behind the crystallized core.

The new planet is also likely to have oxygen as well as carbon. The planet's high density suggests that other lighter elements like hydrogen and helium are not present. Scientists have not found out what this strange diamond planet would look like close up.

"In terms of what it would look like, I don't know I could even speculate," said Ben Stappers of the University of Manchester. "I don't imagine that a picture of a very shiny object is what we're looking at here."