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Bling of Planetary Proportions Only 900 Light-Years Away

ByTim De ChantNOVA NextNOVA Next

Pulsar PSR J2222−0137 is a bag of curiosities. It’s one of the closest known neutron stars, just 900 light-years away. It rotates only 30 times a second, a relative slow-poke among pulsars, which can spin up to thousands of times per second. And it’s orbited by a 10 decillion carat diamond.

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That’s 10 million billion billion billion carats, making it one of the largest diamonds ever discovered.

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A field of white dwarfs, captured by the Hubble Space Telescope

Astronomers studying the nearby pulsar noticed that the radiation it emitted wasn’t reaching Earth when they expected. While unusual, the phenomenon, known as the Shapiro delay, isn’t uncommon. Electromagnetic radiation can be bent by large masses, lengthening the time it takes to reach the Earth. By carefully measuring the distance to the pulsar and the delay of its radio waves, the delay told astronomers something was orbiting PSR J2222, and they had a pretty good idea of how big it was.

Nadia Drake, writing at No Place Like Home:

They calculated that the companion must be about 1.05 times as massive as the Sun (within the range of both a white dwarf and a neutron star), and that the pulsar was slightly more massive, at 1.2 Suns. But scientists also determined that the pulsar and its friend were in a roughly circular, rather than elliptical (or eccentric) orbit. That suggested the system hadn’t been walloped by something like a second, neutron star-forming supernova.

“If there were two neutron stars that means two supernova explosions. And a supernova explosion should make the orbit pretty eccentric,” says study coauthor David Kaplan of the University of Wisconsin, Madison. “We see that the orbit is very circular.”

That circular orbit allowed them to rule out a neutron star, leaving a white dwarf as the remaining possibility. We can often see white dwarfs, but no one could see this one. They stared at the pulsar with the SOAR telescope in Chile, trying to spot the thing in infrared. They also trained the Keck telescope on it, hoping they could catch a glimpse using the two giant, 33-foot mirrors. No luck.

Which meant one thing—the white dwarf was so cool that it had dipped below 3000 K, making it all but invisible. It also means it’s one of the coolest white dwarfs ever detected. The once superheated body had burned through its hydrogen and helium, fused the gases into carbon and oxygen, and then chilled to the point of crystallization, transforming the star into one colossal diamond. Bling-bling.

Image credit: NASA and H. Richer (University of British Columbia)

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