Astronomers in the US have discovered an Earth-sized ‘diamond’ about 900 light-years away in space.

The team of scientists say that the former star – the coldest, faintest white dwarf ever detected - is so cool that its carbon has crystallised to form, essentially, a gigantic diamond in space.

White dwarves are formed at the end of the lifespan of a low- or medium-mass star and are one of the densest forms of matter known to exist. They form when stars, similar in size to our Sun, burn up all of the hydrogen in their cores into helium through nuclear fusion. Gravity then causes the star to collapse inwards, and they slowly cool and fade over time.

The white dwarf was discovered using telescopes from the National Radio Astronomy Observatory and is believed to be about 11 billion years old – about the same age as the Milky Way.

Professor David Kaplan of the University of Wisconsin-Milwaukee described the white dwarf as a “really remarkable object” and said that they are very difficult to detect.

These things should be out there, but because they are so dim they are very hard to find.

Although much cooler than when it was a star, the team calculates that the white dwarf’s temperature is around 2,700 degrees Celsius.

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Observations of the dwarf’s companion pulsar (a rapidly-spinning neutron star) led observers to identify its location as being about 900 light-years away from Earth in the direction of the Aquarius constellation (which is comprised of very faint stars and seen in the southern hemisphere from Earth).