Earth-Size Diamond Detected in Space by Astronomers

A team of astronomers has identified the coldest, faintest white dwarf star that is approximately 11 billion years old.

Using the National Radio Astronomy Observatory's (NRAO) Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA), David Kaplan along with his colleagues at the University of Wisconsin-Milwaukee, successfully identified the star that is the coldest and faintest white dwarf  ever detected. This ancient stellar remnant is believed to be so cold that its carbon has crystallized forming an Earth-sized diamond in space.

"It's a really remarkable object," said David Kaplan, a professor at the University of Wisconsin-Milwaukee. "These things should be out there, but because they are so dim they are very hard to find."

Consisting of carbon and oxygen, white dwarfs are considered to be the remnants of a star like our Sun that gradually diminished over billions of years. This earth-sized diamond in the space is believed to be nearly 11 billion years old.

They detected this celestial gem by observing a pulsar companion to the white dwarf dubbed PSR J2222-0137. Pulsars are the rapidly spinning neutron stars, the remains of the stars that have exploded as supernovas.

It was two years ago that the astronomer Adam Deller using VLBA observed the pulsar that was 900 light years away in the constellation Aquarius. Using Einstein's theory of relativity the researchers studied how the gravity caused delays in the radio signals as the pulsar passed behind the star. Studying the delay in the radio signals the researchers determined the orientation of the orbit as well as the individual masses of the two stars. The mass of the pulsar was 1.2 times that of the Sun and the companion mass was 1.05 times that of the Sun.

After confirming that the pulsar's companion was just another neutron star, the researchers then identified it to be a white dwarf. The astronomers believed that they would be able to observe the companion of the dwarf star in infrared light knowing the distance and brightness of a typical white dwarf star.

Surprisingly, neither the Southern Astrophysical Research telescope in Chile nor the 10-meter keck telescope in Hawaii could detect it.

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

The calculations reveal that the white dwarf is not more than 3000 degrees kelvin colder, i.e. 5,000 times cooler than the Sun.

The finding appears in The Astrophysical Journal.