This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Astronomers have discovered the first example of a second-generation planet orbiting a white dwarf, a world that appears to have formed from the remains of the dead star it now orbits. A team of astronomers led by the University of Warwick has identified the first second-generation planet ever found around a white dwarf.
While similar "reborn" worlds have been suspected to exist around pulsars, this discovery shows that a second generation of planets can form around this much more common stellar remnant. First author Jamie Williams, a Ph.D. student in the Department of Physics at the University of Warwick, said, "Second-generation planets are worlds that form out of the material a star casts off as it dies. They're incredibly rare, and finding one around a white dwarf was completely unexpected.
It's a bit like finding a planet that has risen from the ashes of the very star it once orbited." White dwarfs (the collapsed cores left behind when stars run out of fuel) are known to pull in nearby material from planets, which can be detected in their atmospheres. This chemical signature can tell astronomers details about the planets that are in orbit, and the signal is typically dominated by rock-forming elements like silicon and iron. Published in Nature Astronomy, the study focuses on the white dwarf HS 0209+0832, whose atmosphere contains an unusual chemical signature.
It showed unusually heavy elements including zinc, copper and, most notably, niobium, found at levels over 1,000 times higher than the sun's. These are all elements created during the death of a star, and this is the first time niobium has been found in a white dwarf. Nicholas Stone, of the Department of Astronomy at the University of Wisconsin-Madison, said, "This pattern of elements is a telltale sign of the 's-process', a nuclear reaction that builds heavy elements inside dying stars during their bloated red giant phase.
It's a chemical signature no ordinary, 'first-generation' planet should carry, which told us that this new planet was something different." The team believes the most likely explanation is that the white dwarf, HS 0209+0832, is feeding off a newly formed, second-generation giant planet—one that condensed out of a new disk of material formed during the star's death. Because that disk was made from the star's own expelled material, it would naturally be rich in the unusual heavy elements now showing up in the white dwarf's atmosphere. Williams added, "Forming the protoplanetary disk in this situation is not easy and helps explain why these planets are so rare.
A single, isolated star dies and sheds mass in a roughly symmetrical way. To form a disk of material necessary to birth a planet, HS 0209+0832 likely required a companion star that pulled the ejected material back into orbit, rather than letting it escape." Data from NASA's TESS satellite provided further evidence. Researchers detected a faint, regular brightness signal directly from the planet that was repeating every 4.4 days, which is consistent with a Jupiter-sized gas giant tidally locked in a tight orbit.
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