In what can be called a gem of a discovery, astronomers found a rare planet made of diamonds, which would likely have oxygen apart from carbon. The carbon-based planet lies 4,000 light years away, in the constellation of Serpens in our Milky Way galaxy.

The new planet, which is far denser than any other known so far, races around a tiny unusual star called a pulsar. The planet's high density suggests that lighter elements like hydrogen and helium are not present.

This confluence of extraordinary factors led the researchers at the University of Manchester to believe they had stumbled across something unprecedented. A diamond forms when carbon is put under immense pressure.

The Parkes radio telescope revealed a spinning star called a pulsar, which emits a beam of radio waves, said Michael Keith of CSIRO Astronomy and Space Science, and a member of the research study.

The planet 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, Keith said.

To find the largely carbon-based planet, astronomers from Australia, Germany, Italy, the UK and the U.S. used the Parkes 64-meter radio telescope in western New South Wales.

Scientists speculate that the conditions are right for the carbon within it to be crystallized -- in other words, a giant celestial diamond -- and believe it to be completely made of diamond.

The diamond planet, which is being dubbed as PSR J1719-1438, measures up to 60,000 km across, is about five time Earth's diameter and about 300 time heavier, as indicated by the astronomers' measurements. It orbits the pulsar in just two hours and 10 minutes.

It is believed to be the remnant of a once-massive star that lost its outer layers to the pulsar it orbits, leaving behind the crystallized core.

Pulsar J1719-1438 is a very fast-spinning pulsar -- what's called a millisecond pulsar. It rotates more than 10,000 times per minute, has a mass of about 1.4 times that of our sun but is only 20 kilometers in diameter. About 70 per cent of millisecond pulsars have companions of some kind.

Astronomers believe it is the companion that, in its star form, transforms an old, dead pulsar into a millisecond pulsar by transferring matter and spinning it up to a very high speed. The result is a fast-spinning millisecond pulsar with a shrunken companion - most often a so-called white dwarf.

The study was led by Professor Matthew Bailes of Swinburne University of Technology in Australia and published in the journal Science.

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 Bailes.

In addition, the discovery also raised question of whether there are other diamond planets studding the Milky Way galaxy like jewels on a tiara. Maybe. This is the only one like it so far, Bailes told TIME magazine.

The international research team first detected an unusual star called a pulsar, a tiny dead neutron star that spins around hundreds of times a second and emits beams of radiation.

Irregular movements in the beams gave scientists the hint that there was a companion planet orbiting the pulsar, which then led them to the diamond planet. Astronomers said only two of the 1,800 known pulsars concealed planets and it is the first diamond planet ever seen.

Researchers involved were not certain what the planet would look like up close. The astronomers believe the diamond planet is all that remains of a once massive star, but most of its matter has been siphoned off towards the pulsar it orbits.

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

After finding the planet made of diamonds that is likely to have oxygen, will an expedition to know more about it or collect samples be planned? Since the planet lies 4,000 light years away, it makes such a journey almost impossible. Close-up pictures of the diamond planet are expected from the researchers in the coming months.