Astronomers Identify Earth-Size 'Diamond' in Space

A team of astronomers has identified an Earth-sized "diamond" in space, or possibly the coldest, faintest white dwarf star ever detected.

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

Kaplan and his colleagues found this ancient stellar gem using the National Radio Astronomy Observatory's (NRAO) Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA), as well as other observatories.

White dwarfs, remnants of stars like our Sun, slowly cool and fade over billions of years. This diamond white dwarf - which is so cool that its carbon has crystalized just like a diamond - is likely 11 billion years old.

To detect this celestial gem, researchers looked at the pulsar companion to this white dwarf, dubbed PSR J2222-0137. Pulsars are rapidly spinning neutron stars - the remnants of a violent supernova explosion.

Over the past two years, Kaplan and his colleagues used the VLBA to detect pulsing radio waves emitting from the pulsar. They studied how the gravity of the supposed cool white dwarf warped space, causing delays in the radio signal as the pulsar passed behind it. These delayed travel times helped researchers determine the orientation of their orbit and the individual masses of the two stars.

After ruling out the option that the pulsar's "companion" was just another neutron star, the team realized it must be a white dwarf - only they didn't observe it in optical and infrared light like they should have been able to.

Remarkably, neither the Southern Astrophysical Research (SOAR) telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to 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 fellow researcher Bart Dunlap.

"If there's a white dwarf there, and there almost certainly is, it must be extremely cold."

Researchers speculate that the white dwarf would be no more than a comparatively cool 2,700 degrees Celsius (4,892 degrees Fahrenheit) - that's 5,000 times cooler than the Sun's center.

A paper describing these results is published in the Astrophysical Journal.