[LINK] "The Coldest White Dwarf Ever Discovered Is An Earth-Sized Diamond"

[rfmcdonald]

io9's George Dvorsky highlighted some pretty remarkable astronomical research. As described in the paper "A 1.05 M⊙ Companion to PSR J2222-0137: The Coolest Known White Dwarf?", the aforementioned pulsar PSR J2222-0137 has a white dwarf companion.

This pulsar, dubbed PSR J2222-0137, was detected by Jason Boyles of West Virginia University in Morgantown using the Green Bank Telescope (GBT). The object is about 900 light-years away and it spins more than 30 times each second.

Further analysis showed that it wasn't alone; this pulsar was gravitationally bound to something. Astronomers figured that it was another neutron star, or more likely a white dwarf. The two were calculated to orbit one another every 2.45 days.

To confirm that it was a white dwarf, the researchers applied Einstein's theory of relativity. They studied how the gravity of the companion star warped space, causing delays in the radio signal as the pulsar passed behind it. Delays in travel times allowed the astronomers to determine the precise orientation of their orbit and the individual masses of the two stars; the pulsar has a mass 1.2 times that of our Sun, while the companion has a mass 1.05 times that of the Sun.

[. . .]

Fascinatingly, the astronomers figured that the white dwarf should be detectable in optical and infrared light. So they tried to use the Southern Astrophysical Research (SOAR) telescope in Chile and the 10-meter Keck telescope in Hawaii to detect it, but those surveys yielded nothing. It's that dim.

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

The paper suggests that the white dwarf is also noteworthy for being massive, by the standards of white dwarfs. And only 900 light years away!