Twinkling in the sky is a diamond star of 10 billion trillion trillion carats, astronomers have discovered.

The cosmic diamond is a chunk of crystallised carbon, 4,000 km across, some 50 light-years from the Earth in the constellation Centaurus.

It's the compressed heart of an old star that was once bright like our Sun but has since faded and shrunk.

Astronomers have decided to call the star "Lucy" after the Beatles song, Lucy in the Sky with Diamonds.