Extremely Cold White Dwarf Could Be Earth-Sized Diamond in Space

Posted on June 24, 2014

Astronomers believe they have located an extremely cold white dwarf star. The astronomers say it is possibly the coldest, faintest white dwarf star ever detected. They say it is so cold that its carbon has crystallized, forming an Earth-sized diamond in space.

The astronomers say the white dwarf is likely the same age as the Milky Way, about 11 billion years old. It is located about 900 light-years from Earth. Astronomers found the white dwarf using the National Radio Astronomy Observatory's (NRAO) Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA), as well as other observatories.

The white dwarf was located after its pulsar companion (PSR J2222-0137) was discovered. The pulsar companion was found using the GBT by Jason Boyles, who was then a graduate student at West Virginia University in Morgantown. An artist impression of a white dwarf star in orbit with pulsar PSR J2222-0137 is pictured above.

Boyles' observations with the GBT revealed the pulsar was spinning over 30 times each second and that it was gravitationally bound to its companion star. The pulsar was observed over a two-year period with the VLBA by Adam Deller, an astronomer at the Netherlands Institute for Radio Astronomy (ASTRON). These observations pinpointed its location and distance from the Earth. This data was used to time the arrival of the pulses at the Earth with the GBT.

The researchers studied how the gravity of the companion star warped space, causing delays in the radio signal as the pulsar passed behind it. The delayed signal times helped the researchers calculate the individual masses of the two stars.

The astronomers found that the pulsar has a mass 1.2 times that of the Sun and the companion has a mass 1.05 times that of the Sun. Astronomers say this indicates the companion could not be a second neutron star as the orbits are too orderly for a second supernova to have taken place. The astronomers believed they should have been able to observe the companion in optical and infrared light. However, neither the Southern Astrophysical Research (SOAR) telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to detect it.

Bart Dunlap, a graduate student at the University of North Carolina at Chapel Hill, says in a statement, "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."

A research paper on the extremely cold white dwarf, published in the Astrophysical Journal, can be found here.

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