A star hundreds of light-years away in space may have spawned a giant Jupiter-size planet from the gas and dust it coughed out with its dying breath.
Astronomers spotted signs of such a planet circling a white dwarf — the leftover core of a medium-size star after it burns through its nuclear fuel — called HS 0209+0832.
Though a team of researchers used data from NASA‘s Hubble and TESS telescopes to build a strong case for the planet, no observatory has seen the world itself. For now, it remains a candidate planet. But if the evidence bears out, its discovery would mean stars similar to our sun can launch a fresh round of planet formation after death.
The findings, published in the journal Nature Astronomy, fly in the face of what astronomers expect from dead stars. Before our sun dies, it will likely swell into a red giant and swallow up Mercury, Venus, and Earth in the process. That late-life stage would mark the end for the inner solar system planets the sun birthed long ago. The potential for a second generation raises new questions about whether planets around dead stars could support life. Until now, scientists had only linked planets like this to pulsars, a different type of collapsed star.
“Rather than the white dwarf stage being a kind of epilogue to the story of a star and its planets, this research points to the systems we are familiar with only being the first chapter of a potentially much longer tale,” said Jamie Williams, a doctoral candidate at the University of Warwick in the United Kingdom and the lead author, in a statement, “with some new characters showing up.”
The clues came from debris falling onto the dead star. Between 25 to 50 percent of young white dwarfs pull in debris from nearby objects, according to an associated commentary by Zifan Lin, a planetary scientist at Washington University in St. Louis. That rubble leaves chemical fingerprints in the star’s light and reveals what it contains.
The fingerprints of most white dwarfs match Earth rock or common meteorites, but this star breaks that pattern. Researchers found almost no silicon or iron, the main ingredients of rocky planets like ours. In fact, the mix matches nothing in our solar system, including Halley’s comet. Instead, they detected carbon, nickel, copper, zinc, and niobium — an element that threw a major curveball at the team.
It was this element that led the scientists to the source. Stars forge most of their niobium late in life and disperse it when they molt their outer layers. Some of those cast-offs may have settled into a flat, rotating disk around the young white dwarf, allowing a gas giant planet to emerge from it. Ordinary rocky debris can’t explain the niobium, the extra carbon, or the high ratio of nickel to iron, said Nicholas Stone, a University of Wisconsin theoretical astrophysicist.
“These heavy elements can only be synthesized in the exotic conditions that briefly emerge inside dying stars,” said Stone, a coauthor, in a statement. “The presence of niobium is a signpost of these ‘death’ throes, and the expulsion of the dying star’s innards into space.”
Want more science and tech news delivered straight to your inbox? Sign up for Mashable’s Light Speed newsletter or get Mashable push alerts today.
A companion star may have made the disk possible. Stars near the end of life usually push gas outward evenly in all directions, which leaves little chance for a disk to take shape. But if a small star orbited close by, the swelling giant may have swallowed it. That encounter could have flung the star’s outer layers into a rich ring of material.
Credit: NASA / ESA / Leah Hustak illustration
If this planet truly exists, it could broaden the search for life beyond our solar system. White dwarfs are about the size of Earth, so a planet passing in front of one blocks a large share of its light. That makes an orbiting world’s atmosphere much easier to study. For a rocky, Earth-size planet at a comfortable distance from a nearby white dwarf, the James Webb Space Telescope could detect water, carbon dioxide, and possible signs of life in just a few more passes, Lin wrote.
Right now, the gas giant candidate seems to be rapidly losing its atmosphere. Because the white dwarf is only about 5 million years old, it is still very hot and likely blasting the planet with energy that is whisking away its outer material.
Despite this erosion, the white dwarf will eventually cool and hold a steady temperature, potentially putting the planet in a stable habitable zone for millions of years, according to the research team.
“If the second-generation planet is there, I think it is likely to survive,” Williams said.