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Astronomers Spot 'Phoenix Planet' Born From a Dead Star
By @sharedot · · 8 pages
- Science
- Astronomy
- Exoplanets
- White Dwarfs
Scientists report the first evidence of a second-generation planet orbiting a white dwarf, formed from its dead star's ashes.
A world risen from stellar ashes
Astronomers say they have detected the first known second-generation planet — a world formed not alongside its star, but from the material that star cast off as it died. The candidate planet orbits HS 0209+0832, a white dwarf that was once a star like our sun. "It's a bit like finding a planet that has risen from the ashes of the very star it once orbited," said University of Warwick doctoral student and lead author Jamie Williams. The study was published Monday, October 5 in Nature Astronomy, and co-author Boris Gänsicke of the University of Warwick described a system that "has given birth to a new world using the foundations of the old one."
Why the find was completely unexpected
Second-generation planets have long been theorized — the first exoplanets ever found orbit a pulsar, where any original planets would have been destroyed by a supernova — but none had ever been seen around a white dwarf. "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," Williams said. More than 95% of all stars eventually become white dwarfs, so if confirmed, the discovery suggests dead stellar remnants across the galaxy may host planets nobody thought to look for.
The chemical evidence: niobium and heavy metals
The key clue is the white dwarf's polluted atmosphere. Instead of the ordinary rock-forming signatures of iron and silicon, HS 0209+0832 shows copper, zinc and — for the first time in a white dwarf — niobium, at concentrations around 1,000 times higher than the sun's, per space.com. The researchers say this pattern matches elements forged in the dying star's red giant phase, meaning the material raining onto the dead star's surface cannot be an ordinary first-generation planet. "It's a chemical signature no ordinary, 'first-generation' planet should carry," said study co-author Nicholas Stone of the University of Wisconsin-Madison.
A Jupiter-sized giant on a 4.4-day orbit
Data from NASA's Transiting Exoplanet Survey Satellite (TESS) revealed a faint brightness signal repeating every 4.4 days, consistent with a Jupiter-sized gas giant in a tight, tidally locked orbit around the dead star. Because the white dwarf is extremely hot and blasting out extreme ultraviolet radiation, the planet's atmosphere is being stripped away, and that evaporating material is what carries the heavy-element signature onto the white dwarf's surface. According to CNN, the system lies about 270 light-years from Earth; space.com reports a distance of roughly 790 light-years, and neither figure has been reconciled.
A rare recipe requiring a companion star
The scenario only works under special conditions, which helps explain the planet's rarity. A single dying star ejects its mass symmetrically, so nothing remains to coalesce into a new world. To form the disc of material needed to birth a planet, HS 0209+0832 likely required a companion star — perhaps one around 20% the mass of the sun, or a brown dwarf — that pulled the ejected material back into orbit before it could scatter into space, Williams explained. The astronomers suggest the companion may even have fallen into the star during its giant phase, spinning the debris into the disc from which the new planet condensed.
From candidate to confirmed — and what it means for us
The team stresses this is a candidate, not a confirmed planet. They plan follow-up observations with Hubble and NASA's Chandra X-ray Observatory over the next year and have requested time on the James Webb Space Telescope to pin down the planet's existence and features. "Maybe the Sun will get a new planet someday," said study co-author David J. Wilson of the University of Colorado Boulder.