The “second-generation” world, predicted from telescope data, could be the first known planet of its kind, and it may shed light on the future of our own solar system
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An artistic concept of the second-generation planet orbiting the white dwarf HS 0209+0832
Snehalata Sahu / University of Warwick
In 1999, the Hubble Space Telescope turned its gaze upon a white dwarf—a dense remnant of a star—and detected around 100 mysterious chemical features in its atmosphere. More than two decades later, astronomers have now taken another look at the enigmatic data and realized that it points to the presence of a very unusual cosmic body.
In a study published this week in Nature Astronomy, researchers reveal the possibility that a “second-generation” planet is orbiting the white dwarf. In other words, this world might have been born from the scraps of the dead star. If these findings are confirmed, the planet would be the first of its kind known to researchers and could provide insight into a potential future for our own solar system.
After a small star runs out of nuclear fuel, it sheds its wrapping of gas and dust, leaving behind a core known as a white dwarf. The team suggests that a planet orbiting the white dwarf HS 0209+0832 came together from the accretion of its lost gas and dust, like a sort of astronomical phoenix.
“A phoenix is reborn from the ashes of its predecessor, and this planet is formed from the ashes of the star,” study co-author Jamie Williams, an astronomer at the University of Warwick in England, tells Science News’ Lisa Grossman.
Did you know? White dwarfs
White dwarfs consist of very tightly packed matter. Just one teaspoon of this ultra-dense material would, on Earth, weigh as much as an elephant.
When Williams returned to Hubble’s 1999 data, he noticed that many of the mysterious chemical features could be niobium, a kind of metal used in jewelry and medical imaging devices. As opposed to many common elements, niobium is too heavy to be created by the fusion reactions that happen within a star.
Instead, niobium forms “in the exotic conditions that briefly emerge inside dying stars,” study co-author Nicholas Stone, a theoretical astrophysicist at the University of Wisconsin–Madison, says in a NASA statement. As such, niobium is a marker for stellar death. And while this star’s death throes ejected material, including niobium, out to space, part of it formed into a gas giant planet, the researchers hypothesize.
It’s hard for planets to come together in these conditions, however, which partly explains why second-generation planets are exceptionally rare, Williams adds in a university statement. The gravity of another star was probably necessary to shape the expelled material into a planet-birthing disk.
Hubble recorded unexpected amounts of niobium in the white dwarf. The metal absorbs light, which explains why the telescope detected less light at those wavelengths. NASA, ESA, Leah Hustak (STScI)/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer_public/26/55/26554640-7aa0-41c6-b227-57239f3e4f13/stsci-01m3cdrp9bqc6rab1byk903w93.jpg)
Using NASA’s TESS satellite, the team recognized periodic changes in HS 0209+0832’s brightness that point to an orbiting planet passing in front of it. According to their estimations, this candidate planet—it’s not yet confirmed—is a gas giant with a close orbit of around 3.7 million miles. This is about ten times closer than Mercury’s orbit is to our sun, meaning the planet would be getting blasted by the relatively young white dwarf’s energy. That might be ripping off the planet’s external material and possibly turning it into a disk that rains debris back onto the white dwarf, which would explain why a large amount of niobium made its way into Hubble’s data.
“We know of a large number of white dwarfs that are polluted by planetary material, which is similar in composition to rocks within our solar system,” Sarah Casewell, an observational astronomer at the University of Leicester in England, who did not participate in the study, tells CNN’s Jacopo Prisco. “However, in this case, the white dwarf is polluted by incredibly unusual material, and the composition of this material is similar to atoms we see being created as stars end their lives.”
The illustrated progression of a star’s death and the creation of a second-generation planet NASA, ESA, Leah Hustak (STScI)/https://tf-cmsv2-smithsonianmag-media.s3.amazonaws.com/filer_public/3e/99/3e999e90-66cc-4ef4-962e-f7261fa61a86/stsci-01m3chmxxdapry7d9rw017n188.jpg)
If the planet does exist, its loss of material is not likely to make it wither away entirely. “Eventually the white dwarf will cool and then maintain a consistent temperature, with the planet in its stable habitable zone for millions of years,” Williams says in NASA’s statement.
Moving forward, he plans to continue using Hubble to investigate second-generation planets and how they are born around dead stars. This research marks the first time that astronomers have found niobium in a white dwarf, but it might not necessarily be the last.
If the team’s results are confirmed, they could provide a model for understanding what might one day happen much closer to home. “The sun will eventually become a white dwarf, so we’re also looking at the future of the solar system here,” study co-author David Wilson, an astronomer at the University of Colorado Boulder, tells CNN. “Maybe the sun will get a new planet someday.”
