Scientists have discovered evidence of a star system that might foreshadow the fate of our own.
When stars that aren’t massive enough to end their lifespan in a supernova grow old, they turn into red giants that eventually expel their outer layer of matter. This leaves behind a hot stellar corpse called a white dwarf, which weighs a little less than the Sun but with only a small fraction of the radius. This will likely be the fate of our own Sun. But what will our solar system look like at that point, and what will happen to the planets? Perhaps the answer lies in a new observation that represents the first evidence of a giant exoplanet around a white dwarf.
Scientists have already started to detect disks of dust surrounding white dwarfs, as well as evidence of rocky bodies called planetesimals. This time around, researchers in the United Kingdom, Chile, and Germany took a closer look at what they thought was a pair of white dwarfs in a system called J0914+1914. This pair was first found in a sample of 7,000 white dwarfs taken by the Sloan Digital Sky Survey. But the wavelengths of the light coming from the system revealed materials that wouldn’t normally be found in a pair of white dwarfs alone or even around the subset of “polluted” white dwarfs that show evidence of material falling onto them.
The team then analysed the system using a spectrograph called the X-Shooter on the Very Large Telescope in Chile. These results revealed an abundance of hydrogen, as well as evidence of oxygen and sulfur, which the star is sucking up more than any other elements. These elements are typically found on the ice giant planets in our own solar system, Neptune and Uranus.
Combined with the signature of the motion of the gas, researchers thought that the best way to explain their observations was a giant planet orbiting close to the white dwarf, just 10 million kilometres away from it, and being torn apart into a disk of gas, according to the paper published in Nature.
Perhaps this exoplanet-eating white dwarf system is how our own solar system will look in the future: The progenitor red dwarf expands, swallowing up the inner planets and leaving just the ice giant outer planets behind. But from what we know about this exoplanet, it should have been too close to its star to have survived the initial expansion. “The planet may have migrated there after the red giant dispersed its outsides,” Boris Gänsicke, the study’s first author from the University of Warwick, told Gizmodo.
“This paper is exciting because it reports the detection of a very unusual composition in a white dwarf star,” Johanna Teske, postdoctoral fellow at the Carnegie Institution for Science, told Gizmodo in an email. She also said that the authors did a thorough job of ruling out other potential interpretations of their data. But she pointed out that she was surprised that the paper didn’t contain information on the ultraviolet light that the system emitted, since that is the wavelength most commonly used to study white dwarfs.
And, of course, this is an indirect detection. Gänsicke told Gizmodo that his team has applied for time on the Hubble Space Telescope to look for further evidence of a planet orbiting this white dwarf. And perhaps the planet has a detectable comet-like tail, he said.
This is just one white dwarf. The Gaia satellite has discovered 230,000 white dwarfs, many of which may also be “polluted.”
“There is the potential to not only discover more polluted white dwarfs, but perhaps uncover a wider variety in their compositions,” said Teske. Maybe more of these systems will reveal that they, too, contain leftovers of gas giant planets.
Perhaps our own solar system will one day join that sample.
Featured image: Illustration: ESO