Astronomers have identified what might be one of the strangest stars in our galaxy: an incredibly cold, ancient and faint white dwarf that has crystallized into a diamond the size of Earth.

“It’s a really remarkable object,” said Professor David Kaplan of the University of Wisconsin-Milwaukee in a press release. “These things should be out there, but because they are so dim they are very hard to find.”

White dwarfs are stars at the end of their life span when the fusion reaction that has pumped out heat and energy during has all but stopped, leaving the remaining carbon and oxygen to compact into an incredibly dense and cold state.

Download the new Independent Premium app Sharing the full story, not just the headlines

In the case of this recently discovered white dwarf, astronomers believe that it has cooled and crystallized all the way to diamond, estimating that the once-fiery star is 11 billion years old – making it the same age as the Milky Way.

Shape Created with Sketch. NASA: Space in pictures Show all 12 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. NASA: Space in pictures 1/12 NASA A false colour image of Cassiopeia A comprised with data from the Spitzer and Hubble Space Telescopes and the Chandra X-Ray observatory Nasa 2/12 NASA The Barred Spiral Galaxy (NGC 6217) in the Ursa Minor constellation is pictured in Space 3/12 NASA A team of astrophysicists has detected so-called gravitational waves – predicted by Albert Einstein a century ago – which are the first tremors of the Big Bang when time and space began about 13.7 billion years ago Rex 4/12 NASA The barred spiral galaxy M83, also known as the Southern Pinwheel. The Hubble photograph captures thousands of star clusters, hundreds of thousands of individual stars, and 'ghosts' of dead stars called supernova remnants 5/12 NASA Acosmic creepy-crawly known as the Tarantula Nebula in infrared light 6/12 NASA A spiral galaxy ESO 373-8 - together with at least seven of its galactic neighbours, this galaxy is a member of the NGC 2997 group 7/12 NASA A massive galaxy cluster Abell 2744, according to NASA these are some of the faintest and youngest galaxies ever detected in space 8/12 NASA A giant cloud of solar particles, a coronal mass ejection, explodes off the sun, lower right, captured by the European Space Agency and NASA's Solar and Heliospheric Observatory 9/12 NASA Current conditions of the quiet corona and upper transition region of the Sun 10/12 NASA First color image of the Earth taken by the Apollo 8 astronauts in 1968 11/12 NASA Fog forming over the the US Great Lakes area and streaming southeast with the wind. A swirling mass of Arctic air moved south into the continental United States 12/12 NASA Astronaut Mike Hopkins, Expedition 38 Flight Engineer, is shown in the second of two spacewalks designed to allow the crew to change out a faulty water pump on the exterior of the Earth-orbiting International Space Station 1/12 NASA A false colour image of Cassiopeia A comprised with data from the Spitzer and Hubble Space Telescopes and the Chandra X-Ray observatory Nasa 2/12 NASA The Barred Spiral Galaxy (NGC 6217) in the Ursa Minor constellation is pictured in Space 3/12 NASA A team of astrophysicists has detected so-called gravitational waves – predicted by Albert Einstein a century ago – which are the first tremors of the Big Bang when time and space began about 13.7 billion years ago Rex 4/12 NASA The barred spiral galaxy M83, also known as the Southern Pinwheel. The Hubble photograph captures thousands of star clusters, hundreds of thousands of individual stars, and 'ghosts' of dead stars called supernova remnants 5/12 NASA Acosmic creepy-crawly known as the Tarantula Nebula in infrared light 6/12 NASA A spiral galaxy ESO 373-8 - together with at least seven of its galactic neighbours, this galaxy is a member of the NGC 2997 group 7/12 NASA A massive galaxy cluster Abell 2744, according to NASA these are some of the faintest and youngest galaxies ever detected in space 8/12 NASA A giant cloud of solar particles, a coronal mass ejection, explodes off the sun, lower right, captured by the European Space Agency and NASA's Solar and Heliospheric Observatory 9/12 NASA Current conditions of the quiet corona and upper transition region of the Sun 10/12 NASA First color image of the Earth taken by the Apollo 8 astronauts in 1968 11/12 NASA Fog forming over the the US Great Lakes area and streaming southeast with the wind. A swirling mass of Arctic air moved south into the continental United States 12/12 NASA Astronaut Mike Hopkins, Expedition 38 Flight Engineer, is shown in the second of two spacewalks designed to allow the crew to change out a faulty water pump on the exterior of the Earth-orbiting International Space Station

Stars like this aren’t rare (around 97 per cent of stars are thought to turn into white dwarfs and we've even discovered planets made of diamond) but they are incredibly difficult to find – simply because their light is too faint to make its way through the cosmos to telescopes on Earth.

Thankfully, this particular white dwarf had a partner that gave away its presence to astronomers on Earth: a companion pulsar star dubbed PSR J2222-0137.

Pulsars are superdense neutron stars that spin incredibly quickly, shooting beams of radio waves into the cosmos like supercharged lighthouses. However, with PSR J2222-0137 astronomers noticed that the radio beams were regularly obstructed by an unknown object.

The team from the National Radio Astronomy Observatory in the US suspected it was a white dwarf, but were still unable to see the object after further observation. Their explanation? That this is one of the coldest white dwarf ever discovered.

“Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don’t see a thing,” said University of North Carolina graduate student Bart Dunlap. “If there's a white dwarf there, and there almost certainly is, it must be extremely cold."

However, this is cold in an astronomical sense and despite being 5,000 times cooler than the center of the Sun, the diamond white dwarf is still thought to be 2,700 degrees Celsius (or 4,892 degrees Fahrenheit).