White dwarfs often show signs of metals in their spectra, providing evidence that these evolved stars have accreted planetary material. Could white dwarf spectra also provide evidence for technological activity in these star systems?
A Record of Planets Past
When a Sun-like star reaches the end of its hydrogen-burning lifetime, it first puffs up into a red giant before exposing its white-hot core, which evolves into a white dwarf. This dramatic transition shakes up any planets that happened to be orbiting the star, and some close-in planets may end up crumbling apart, their rubbly remains peppering the surface of the white dwarf.
So far, astronomers have found hundreds of white dwarfs that appear to be polluted with heavy elements from their destroyed planets. These observations provide a valuable look into the bulk compositions of planetary materials outside our solar system. They may also provide a way to detect patterns of chemical abundances that are not natural, resulting from technological processes like industrial refining or the creation of alloys — in other words, a technosignature that is evidence of not just life, but technologically advanced life.
Seeking Signs of Technology
Representation of the chemical abundances of meteorites (pink, orange, and green) and white dwarfs (gray). Most white dwarf abundances overlap with the parameter space defined by the meteorite sample. Click to enlarge. [Huang et al. 2026]
The team used thousands of chemical abundance measurements from meteorites as a reference for the natural bulk composition of planetary material. For the mixture of natural and processed material, they combined the meteorite reference material with a template that is metal-rich and silicate-poor, with enhanced amounts of iron, nickel, chromium, and manganese.
Evidence for a model including technologically processed material relative to a purely natural model, as a function of the number of elements detected in the white dwarf. ndet = 0 indicates that only upper limits were obtained on elemental abundances. Higher Bayes factors indicate stronger evidence. The left-hand plot is based on abundances measured from the white dwarfs’ photospheres, while the right-hand plot uses abundances adjusted for diffusion within the white dwarf. Click to enlarge. [Adapted from Huang et al. 2026]
No Strong Evidence, but a Path Forward
Ultimately, Huang’s team found that strong statistical support for the existence of technological processes was uncommon, though there were certain measurements in their sample of white dwarfs that were difficult to reconcile with a solely natural model.
Perhaps unsurprisingly, the team also found that the quality of the chemical abundance measurements affected the constraining power of the observation; some white dwarfs had upper limits for just a few elements, while others had definitive detections of many elements. They found that the most discerning observations recorded iron, magnesium, chromium, and titanium, plus either nickel, silicon, or sodium.
While this work didn’t dredge up firm evidence for technological activity, it provides a jumping-off point for future searches. The handful of white dwarfs in this sample that were fit poorly by a purely natural model could be compared against other technosignature models or targeted with high-resolution spectroscopy. Future measurements of iron and magnesium in polluted white dwarfs may be useful as a preliminary screening tool, helping to pick out intriguing targets for follow-up observations.
Citation
“A Calibrated Bayesian Search for Potential Chemical Technosignatures in Polluted White Dwarfs,” Bo-Lun Huang et al 2026 ApJ 1006 9. doi:10.3847/1538-4357/ae742c