Astronomers have discovered an unusual planet that appears to have formed from the remains of a dying star, earning it the nickname of a “phoenix planet” after the mythical bird that rises from its ashes.
The exoplanet, which orbits a white dwarf about 250 light years from Earth near the constellation Cetus, is believed to be the first confirmed example of a planet forming around such a stellar remnant.
Researchers described it as a second-generation planet, meaning it formed from material expelled by a dying star rather than from the swirling disk of gas and dust surrounding a newly formed star, as happened with Earth and other planets in our solar system.
“This is the first example of a planet forming around a white dwarf,” said Jamie Williams, a doctoral student in astrophysics at the University of Warwick in England and lead author of the study published in Nature Astronomy.
The planet is a gas giant believed to be slightly more massive than Jupiter, the largest planet in our solar system.
It completes an orbit around its white dwarf host every 4.4 days, at just 4% of the distance between Earth and the Sun.
Its extremely close position exposes it to intense ultraviolet radiation from the white dwarf, causing its outer atmosphere to evaporate, with some of the material eventually falling back into the stellar remnant.
The planet’s chemical composition also provides clues to its unusual origins. It contains high levels of niobium, copper and zinc, elements associated with material expelled by certain stars during their final stages.
This suggests that the planet formed from a disk of debris left behind after its host star died.
“In myths, a phoenix is born again from its own ashes. In the case of this planet, it is born again from the ashes of its dying host star, and therefore the planetary system is reborn,” Williams said.
He explained that a second-generation planet is one that forms after its host star dies, in this case after becoming a white dwarf.
The discovery was made using data from the Hubble, TESS and FUSE space telescopes. Researchers hope to use the James Webb Space Telescope to further confirm their findings.
A small number of potential second-generation planets have previously been identified around pulsars, which are rapidly rotating neutron stars formed from stellar remnants.
However, white dwarfs are far more common than pulsars. Williams said more than 95% of stars in the Milky Way are expected to eventually evolve into white dwarfs, suggesting that second-generation planets could be widespread.
Although the newly discovered gas giant is unsuitable for life, researchers believe rocky planets could also form around white dwarfs and potentially support habitable conditions.
Williams said white dwarfs gradually cool over time, with the cooling process slowing as they age.
If a rocky second-generation planet formed at the right distance, it could remain within the star’s habitable zone for billions of years.
Meanwhile, a separate study published in the same journal has revealed another unusual celestial pairing involving a red dwarf star and a brown dwarf in the constellation Taurus, approximately 300 to 500 light years from Earth.
Using the Zwicky Transient Facility at Palomar Observatory in California, researchers identified a red dwarf with about 8% of the Sun’s mass orbiting a brown dwarf.
The brown dwarf, an object too small to sustain itself as a star but more massive than a planet, has about 30 times Jupiter’s mass and one-third the mass of its stellar companion.
The two objects orbit each other every 87 minutes, separated by slightly more than half the distance between Earth and the Moon.
Researchers believe the red dwarf’s gravity is pulling material away from the brown dwarf, with some of it landing on the star’s surface and creating a detectable hot spot.
“This is the first observed example of this phenomenon,” said Aaron Householder, an astrophysics graduate student at the Massachusetts Institute of Technology and lead author of the second study.
“The two objects are so close together that the entire orbit would fit inside the Sun,” he added.
