A University of Warwick-led study published October 5 in Nature Astronomy reports evidence consistent with a second-generation planet candidate around the white dwarf HS 0209+0832. The study links unusual chemical signatures in material accreting onto the star with a periodic change in its brightness. The paper describes the object as a candidate.
A second-generation planet, in this scenario, would form from material expelled as its progenitor star evolved. The system’s white dwarf is the hot, compact remnant of a star.
The chemical clue in Hubble’s archival spectrum
Hubble recorded an ultraviolet spectrum of HS 0209+0832 in 1999. When researchers reanalyzed it, they matched previously unidentified spectral features to copper and niobium. Observations from FUSE also show strong niobium signatures, according to NASA’s account of the study.
The study reports that material accreting onto the white dwarf is enriched in zinc, copper and niobium. Silicon appears only in trace amounts, while iron was not detected. That unusual chemical pattern is part of the case for material linked to a possible second-generation planet.
What TESS measured
TESS observations recorded a periodic brightness signal with a period of 4.399 ± 0.026 days and an amplitude of 0.120% ± 0.018%. The study considers two possible explanations: changing thermal emission as a planet’s day and night sides rotate into view, or a transiting tail of material from an evaporating gas giant. The study says a giant planet at 0.04 astronomical units could produce the signal; NASA describes the corresponding separation as about 6 million kilometers.
NASA characterizes the candidate as roughly Jupiter-sized and says the hot white dwarf’s radiation is likely stripping away its atmosphere. The study’s measured brightness cycle and chemical evidence inform that interpretation.
Possible paths to a second-generation planet
One possibility is that expelled stellar material formed a disk from which a planet later developed. The paper also discusses another route: an older planetary core could have acquired an atmosphere made from second-generation material. The chemical and brightness measurements inform these possibilities, while the study presents the planet as a candidate.
NASA Goddard’s English-language animation visualizes the proposed stellar-ejecta scenario; its cosmic scale is artistic.
