The Earth is not a perfect sphere. Our planet’s rotation causes it to bulge slightly at the equator, making it 0.3 percent wider there than from pole to pole.
But that’s nothing compared to PSR J2322-2650ban object with a mass comparable to that of Jupiter recently studied by the James Webb Space Telescope. This planet’s equatorial diameter is 38 percent wider than its polar diameter, giving it the strange appearance of a lemon and a very strange atmosphere.
“It is the most elastic planet whose elongation we have confirmed,” said Michael Zhang, an exoplanet scientist at the University of Chicago and lead author of a paper describing the planet, published Tuesday in The Astrophysical Journal Letters.
PSR J2322-2650b was discovered in 2011 by Australia’s Parkes radio telescope. It is located more than 2000 light years from Earth. It was immediately interesting as a Jupiter-sized gas giant orbiting a pulsar, a dense, rapidly spinning star derived from a supernova. Pulsars are so called because they shoot jets of radiation from their poles. The planet is just a million kilometers from the star, completing one orbit in about eight hours. It is the only known gas giant orbiting a pulsar.
This proximity gives the planet its unusual shape as the star’s gravity pulls on it. “It’s close enough that everything is funneled from the object to the pulsar,” said Peter Gao, an exoplanet scientist at the Carnegie Institution for Science in Washington and an author of the paper. “You have a literal tip, like a point, where material leaves the planet and spirals in.”
Using the infrared capabilities of the Webb telescope, the team was able to study the planet’s atmosphere, the first time this has been done for a planet orbiting a pulsar. Such observations hinted at the strange shape of the world. And they also revealed something extremely strange: the planet lacks hydrogen, oxygen and nitrogen, elements common on other planets, including gas giants. Instead, it is made up primarily of helium and molecular carbon. “A world dominated by helium and carbon is something we have never seen before,” Gao said.
Its carbon atmosphere could give it “clouds made of graphite,” Zhang said, and diamonds at its core. Bands of storms would trace the lemon-like, W-shaped exterior of the world, while it would most likely be red in color due to dust and soot-like particles formed by carbon.
“It’s a weird, bizarre thing,” said Emily Rauscher, a theoretical astrophysicist at the University of Michigan, who was not involved in the work. “It hasn’t formed like any other normal planet.”
The strange properties of PSR J2322-2650b could mean that it is not actually a planet, but rather the remnant of a star that orbited the pulsar and has been slowly devoured. “We’re leaning toward the star hypothesis,” Gao said, which could make it a type of system known as a black widow pulsar, in which we see a star devoured by a pulsar.
It could be the last moments of such a system, with PSR J2322-2650b about to be completely consumed. “It would have lost 99.9 percent of its mass, and we have detected it right at the end,” Gao said.
Alternatively, Zhang said it could also be “a completely new type of object that we don’t have a name for,” in which PSR J2322-2650b would remain in a stable orbit around its pulsar for billions of years, rather than being imminently devoured. He hopes to search for more such worlds in the future to find out.
“I hope we have a brother to compare this object to,” he said. “If it is continually losing mass, we have had to be very lucky to see it in its last breath before disappearing.”