Niobium in old Hubble spectra points to a planet that may have formed after its star died

A white dwarf is what remains of a low-mass star's core after the star has exhausted its fuel and shed its outer layers into space ^[13]. The case for a planet built from those layers rests on niobium, because of where that element is made. "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," said Nicholas Stone, a theoretical astrophysicist at the University of Wisconsin-Madison and a member of the team ^[6]. "The presence of niobium is a signpost of these 'death' throes, and the expulsion of the dying star's innards into space," Stone said ^[7]. According to Williams, the unusually large amount in this system may trace matter expelled during the star's death, not material left over from its birth ^[12].

The Nature Astronomy study, published Oct. 5, builds its claim in three steps of unequal strength ^[1]. Identifying the element is the firmest step, since data from two separate instruments show it ^[4][9]. TESS supplies only a candidate planet, inferred from changes in the star's brightness ^[10]. The last step, that some of the expelled material gathered into a gas giant while the rest dispersed, is the team's proposal ^[8]. The release does not say how the researchers excluded a planet that formed with the star and survived its death.

"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 analyzed to date," said Boris Gaensicke, a co-author also at the University of Warwick ^[14]. That comparison counts only white dwarfs in which someone has identified the element. Williams said the niobium signature was one "I was unfamiliar with when I first found it in the archival data" ^[5]. In this system, the niobium went unidentified from the 1999 observation until the 2026 study, a gap of about 27 years ^[3][16].

We think the niobium is the solid finding here. The second-generation planet is a hypothesis built on it, and it depends on the TESS candidate being confirmed. Williams framed the stakes more widely. "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," Williams said ^[15].