Astronomer David Kaplan, of the University of Wisconson-Milwakee and his colleagues believe that they have found the coldest, faintest white dwarf star ever detected.

White dwarves are stars which used to be similar to our Sun. After the stars expand to become a red giant, they begin to collapse into an extremely dense ball of carbon and oxygen roughly the size of the Earth. The stars slowly cool and fade over billions of years. The researchers believe that this particular star is roughly the same age as the Milky Way galaxy, or roughly 11 billion years old.

“It’s a really remarkable object. These things should be out there, but because they are so dim they are very hard to find,” said Kaplan in a statement.

One of the reasons that this particular white dwarf was easier to find is that it is part of a binary star system. It’s companion is a pulsar , PSR J2222-0137, which was the first of the two objects to be discovered.

Pulsars are the extremely dense remains of a supernova. These stars spin incredibly quickly sending out lighthouse-like beams of radio waves from the poles. The original observations of this particular pulsar, made by radio telescopes, revealed that it was spinning more than 30 times per second and that it was gravitationally bound to another star.

The pulsar was studied for two years using the Very Long Baseline Array (VLBA), by astronomer Adam Deller of the Netherlands Institute for Radio Astronomy (ASTRON). Deller was able to pinpoint the location of the binary system at roughly 900 light-years from Earth in the direction of the constellation Aquarius.

By using Dellers observations and applying Einstein’s theory of relativity, researchers were able to learn more about the pulsars companion star by the delays in the pulsar’s radio signal. The pulsar was determined to have 1.2 times the mass of the Sun and its companion 1.05 times.

Once the researchers knew the location and type of star that they were looking for, they hoped to be able to observe it optically using infrared telescopes. However it could not be found with either the Southern Astrophysical Research (SOAR) telescope in Chile or the Keck telescope in Hawaii.

“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. If there’s a white dwarf there, and there almost certainly is, it must be extremely cold,” said Bart Dunlap, a graduate student at the University of North Carolina at Chapel Hill and one of the team members.

The lack of infrared signal told the researchers that the star must be very cool. The diamond star is believed to be roughly 3,000 degrees Kelvin, which doesn’t sound very cool. It is, however, 5000 degrees cooler than our Sun at its core.

The cool star, composed largely of crystalized carbon, would be very similar to a diamond. It has long been believed that such objects existed but their low temperature and dim light make them very difficult to locate.

The researchers findings can be found, in detail, in the Astrophysical Journal.