Astronomers Identify Second Generation Planet Around White Dwarf

Astronomers have identified evidence of a possible second-generation planet around white dwarf HS 0209+0832 using NASA Hubble Space Telescope data and other observations. The study, published in Nature Astronomy, found chemical signatures suggesting a gas giant formed from material expelled by a dying star.

According to NASA and the European Space Agency, researchers revisited Hubble observations from 1999 that contained about 100 unidentified chemical features. They linked many of those signals to niobium and other elements produced during a star's death process.

The team estimates the candidate planet is a gas giant about the size of Jupiter, according to the research released by NASA and ESA. It orbits about 3.7 million miles (6 million kilometers) from the white dwarf and is rapidly losing atmosphere.

Jamie Williams, astronomer and lead author from the University of Warwick in the United Kingdom, described the finding as evidence that planetary systems can continue evolving after a star reaches the white dwarf stage.

"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, with some new characters showing up. That’s a really exciting prospect to pursue," said Jamie Williams, astronomer and lead author, a doctoral candidate at the University of Warwick in the United Kingdom.

Williams said the discovery centered on unusual chemical evidence found in archived Hubble data. The element niobium became a key clue after researchers compared the observations with updated chemical databases.

"What Hubble is showing us in this white dwarf system is something we haven’t seen before: a high abundance of the element niobium, the signature of which I was unfamiliar with when I first found it in the archival data," said Jamie Williams, astronomer and lead author, a doctoral candidate at the University of Warwick in the United Kingdom.

The research team found that niobium and other heavy elements could indicate material created during the dying star's final stages. Nicholas Stone, a theoretical astrophysicist at the University of Wisconsin – Madison and member of the research team, explained the significance of the chemical signature.

"Niobium and other elements heavier than iron are astronomically special because, unlike many common elements, they are not formed in the cores of stars by thermonuclear fusion. Instead, these heavy elements can only be synthesised in the exotic conditions that briefly emerge inside dying stars. The presence of niobium is a signpost of these ‘death’ throes, and the expulsion of the dying star’s innards into space," said Nicholas Stone, theoretical astrophysicist at the University of Wisconsin – Madison and member of the research team.

The researchers theorize that some of the expelled material later combined into the possible gas giant, while the remaining material dispersed. The planet's atmosphere loss may create a trail of material around the white dwarf that contributes to the observed chemical signatures.

"When Jamie asked me about niobium in relation to this study I was truly gobsmacked, as that element had not been reported in any other white dwarf analysed to date. Once we realised it was there, everything fell into place," said Boris Gaensicke, astronomer and study co-author.

Data from NASA's retired FUSE mission confirmed the niobium signatures, while NASA's TESS mission observed brightness variations from the system for four months. The researchers said the planet may survive as the white dwarf cools over time.

"If the second-generation planet is there, I think it is likely to survive. Eventually the white dwarf will cool and then maintain a consistent temperature, with the planet in its stable habitable zone for millions of years," said Jamie Williams, astronomer and lead author, a doctoral candidate at the University of Warwick in the United Kingdom.

Williams said further research will examine how second-generation planets form, how common they are, and how they evolve around stellar remnants. The team plans to continue studying these systems with Hubble observations.

"I think this research is an important example of the fact that scientific discovery is not a straight path. It often needs that magical moment when people discuss big questions on their minds and realise that together they can find unexpected answers," said Boris Gaensicke, astronomer and study co-author.