Likely detection of water-rich asteroid debris in a metal-polluted white dwarf

TL;DR

This paper reports the detection of water-rich asteroid debris in a metal-polluted white dwarf, suggesting that water-bearing planetary material can significantly pollute white dwarf atmospheres over time.

Contribution

It provides evidence for water-rich planetary debris accretion in white dwarfs, expanding understanding of planetary system evolution and composition.

Findings

White dwarf shows signs of water-rich asteroid debris.

Accreted debris contains approximately 38% water by mass.

High accretion rate indicates significant ongoing material influx.

Abstract

The cool white dwarf SDSS J124231.07+522626.6 exhibits photospheric absorption lines of 8 distinct heavy elements in medium resolution optical spectra, notably including oxygen. The Teff = 13000 K atmosphere is helium-dominated, but the convection zone contains significant amounts of hydrogen and oxygen. The four most common rock-forming elements (O, Mg, Si, and Fe) account for almost all the accreted mass, totalling at least 1.2e+24 g, similar to the mass of Ceres. The time-averaged accretion rate is 2e+10 g/s, one of the highest rates inferred among all known metal-polluted white dwarfs. We note a large oxygen excess, with respect to the most common metal oxides, suggesting that the white dwarf accreted planetary debris with a water content of ~38 per cent by mass. This star, together with GD 61, GD 16, and GD 362, form a small group of outliers from the known population of evolved planetary systems accreting predominantly dry, rocky debris. This result strengthens the hypothesis that, integrated over the cooling ages of white dwarfs, accretion of water-rich debris from disrupted planetesimals may significantly contribute to the build-up of trace hydrogen observed in a large fraction of helium-dominated white dwarf atmospheres.