white Dwarf Reveals Consumption of Icy Planetesimal, Echoing Pluto’s Composition
Recent observations of the white dwarf WD 1647+375 have revealed compelling evidence that the star has been consuming a frozen planetesimal, possibly a fragment of a Pluto-like dwarf planet from another star system. The findings, published January 27, 2025, in the Monthly Notices of the Royal Astronomical Society (Leicester, Bekki & Tsujimoto, 2025), mark the first unambiguous detection of a white dwarf accreting icy material.
White dwarfs, the dense remnants of sun-like stars, frequently enough pull in debris from surrounding planetary systems. By analyzing the chemical composition of a white dwarf’s atmosphere, astronomers can deduce the nature of the material it has absorbed. Typically, this reveals evidence of rocky material like calcium and other metals. However, WD 1647+375 presented a different story.
“In this way, white dwarfs act like cosmic crime scenes – when a planetesimal falls in, its elements leave chemical fingerprints in the star’s atmosphere, letting us reconstruct the identity of the ‘victim’,” explained researchers.
ultraviolet spectroscopy revealed a surprisingly high abundance of nitrogen – approximately 5% of the accreted mass – the highest ever detected in a white dwarf. The atmosphere also contained 84% more oxygen than would be expected from solely rocky material, both indicators of an icy composition.
Data indicates that the white dwarf has been steadily consuming debris for at least the past 13 years, at a rate of roughly 200,000 kg (equivalent to the weight of an adult blue whale) per second. This suggests the planetesimal is at least 3 kilometers in diameter, tho the ongoing accretion over potentially hundreds of thousands of years means its original size could be as large as 50 kilometers. The object is estimated to be composed of approximately 64% water.
Professor Boris T. Gänsicke, of the Department of Physics at Warwick University, likened the planetesimal to objects found in our own solar system’s kuiper Belt, beyond Neptune. “We think that the planetesimal absorbed by the star is likely to be a fragment of a dwarf planet like Pluto,” he stated. “This is based on the nitrogen-rich composition, high predicted mass, and 2.5 high ice-rock ratio, which is more than a typical KBO and is likely to originate from crust or planetary coat like Pluto.”
The origin of the icy body remains uncertain – whether it formed within the original star system or was captured from interstellar space. Nonetheless, the finding provides strong evidence for the existence of cold, water-rich bodies in planetary systems beyond our own.
the research also highlights the importance of ultraviolet spectroscopy in analyzing the composition of these rare objects, as UV light is crucial for detecting volatile elements like carbon, sulfur, oxygen, and nitrogen – key building blocks for life.
Reference: leicester, B., Bekki, K., & Tsujimoto, T. (2025). Chemical enrichment by Rolrapsars as Unusual High Origin (BA/Fe) in the Galaxy NGC 1569 big star. Monthly Notices of the Royal astronomical Society.Doi: 10.1093/mnras/staf142
