A dead star’s wreckage may be the birthplace of a new planet. The existence of second-generation planets was predicted theoretically more than 15 years ago. But this “phoenix” world, if confirmed, would be the first actually spotted, scientists report October 5 in Nature Astronomy.
The finding suggests planetary systems can have a second life even after their stars die. Before this discovery, this planet formation process has been “more like a hypothesis, more like speculation,” says planetary scientist Zifan Lin of Washington University in St. Louis, who was not involved in the new work.
White dwarfs are the small, dense cores left behind after low-mass stars — like our sun — puff up into red giant stars at the end of their lives, ultimately blowing all the outer material away. These stellar corpses are so dense that most chemical elements sink into their centers, leaving them with pristine atmospheres composed of almost entirely hydrogen and helium. But astronomers have found that between a quarter and half of these stars are “polluted” with elements like silicon and iron, which are found in rock.
These elements probably come from shattered planets that the star devoured as it expanded. Astronomers have also found whole planets that seem to have survived their stars’ demise and still orbit the remaining white dwarf. Ironically, some astronomers think these dead stars could be prime hunting grounds for signs of extraterrestrial life.
HS 0209+0832 was a known weirdo. When the Hubble Space Telescope observed it in 1999, astronomers could tell that the white dwarf contained a mysterious mix of chemicals, but they couldn’t identify them. Since then, there have been more detailed studies of how certain atoms would show up in stellar atmospheres, Williams says.
Reanalyzing those observations showed that the white dwarf contains only trace amounts of silicon and almost no iron, Williams and colleagues found. But it does include a ridiculous amount of niobium. This hard, silvery metal, used in jewelry, rocket systems and superconductors, is rare on Earth and had never been seen in a white dwarf.
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