This Giant Planet Is Orbiting a Dead Star
In a first, NASA astronomers have discovered a planet orbiting a ‘dead’ white dwarf star
When small stars the size of our sun die, they go out with a bang. As the star runs out of hydrogen fuel, it cools and expands to become a gargantuan red giant. After ejecting up to 80 percent of its mass in a protracted explosion, the star will collapse in on itself, leaving behind a small core that slowly continues to cool.
The death of a star tends to incinerate its surroundings—for instance, scientists predict that when our own sun dies in about 5 billion years, it will destroy Mercury, Venus, and likely Earth, Jackson Ryan reports for CNET.
However, in a major find, NASA researchers announced last week that they’ve discovered a planet orbiting a “dead” white dwarf star. The discovery indicates that the planet may have remained intact during its star’s explosive death and “lived” to tell the tale, reports Ashley Strickland for CNN.
Lead author Andrew Vanderburg, an astronomer at the University of Wisconsin-Madison, and his team published their find in Nature. The team used NASA’s Transiting Exoplanet Survey Satellite (TESS) and the now-retired Spitzer Space Telescope, as well as many on-ground observations, to confirm the find.
Vanderburg’s team discovered a planet orbiting WD 1856+534, a small white dwarf star that lies in the Draco constellation about 80 light years away from Earth. The planet, dubbed WD 1856 b, is a gas giant roughly the size of Jupiter. Compared to its star, the planet is massive: about seven times its size. It circles the star very closely and makes a complete orbit about every 34 hours, per a NASA statement.
In the study, the authors estimate that WD 1856 is about ten billion years old. About six billion years ago, it began to die, expanding to giant, destructive proportions.
WD 1856 b might have originated at least 50 times farther away from its present location, the researchers estimate in their study. But astronomers don’t know for certain how WD 1856 b survived its stars decline, and what pushed the planet so much closer to the star, Mike Wall reports for Space.com.
“WD 1856 b somehow got very close to its white dwarf and managed to stay in one piece,” Vanderburg says in the NASA statement. “The white dwarf creation process destroys nearby planets, and anything that later gets too close is usually torn apart by the star’s immense gravity. We still have many questions about how WD 1856 b arrived at its current location without meeting one of those fates.”
Usually, a star’s death will pull nearby asteroids and planets inward and destroy them, creating a disk of debris that surrounds the planet. “That’s why I was so excited when [Vanderburg] told me about this system,” says study co-author Siyi Xu in the statement. “We’ve seen hints that planets could scatter inward ... but this appears to be the first time we’ve seen a planet that made the whole journey intact.”
According to study co-author Juliette Becker, one theory explaining WD 1856 b’s origins involves several other big planets nearby. These bodies might have impacted the planet’s trajectory as its star exploded.
“The most likely case involves several other Jupiter-size bodies close to WD 1856 b’s original orbit,” Becker notes in the NASA statement. “The gravitational influence of objects that big could easily allow for the instability you’d need to knock a planet inward. But at this point, we still have more theories than data points.”
According to CNET, the find is exciting because it suggests that a “dead” star could potentially host a planet with the right conditions for life. Although WD 1856 b has a “hot, smothering” atmosphere that’s not conducive to life, Vanderburg tells CNN, its discovery opens the door to future research about the habitability of different kinds of exoplanets. White dwarf stars let off heat as they cool, and a planet at the right distance from the star could benefit from sun-like light for long, stable periods of billions of years—some of the necessary ingredients for life as we know it.
“It seems like white dwarf systems may be a pretty good place to live, if your planet happens to be in the right part of the system,” Vanderburg tells CNN. “So if WD 1856 can make it to this part of the system, then maybe other, smaller planets could as well, including the rocky planets we expect to be the best places for life to exist.”