A double debris disc around a white dwarf sculpted by two planetary bodies

N. P. Gentile Fusillo; Felipe Lagos-Vilches; Boris T. Gänsicke; Christopher J. Manser; D. Koester; N. P. Gentile Fusillo

doi:10.1038/s41550-026-03004-3

AI summary · DOI: 10.1038/s41550-026-03004-3 · Physics and Astronomy

A double debris disc around a white dwarf sculpted by two planetary bodies

N. P. Gentile Fusillo, Felipe Lagos-Vilches (University of Warwick, Universidad Técnica Federico Santa María), Boris T. Gänsicke (University of Warwick), Christopher J. Manser (Imperial College London), D. Koester (Christian-Albrechts-Universität zu Kiel), N. P. Gentile Fusillo (University of Trieste, Trieste Astronomical Observatory)

Original paper Published on 26 Oct. 2026 Published in Nature Astronomy (26 Oct. 2026) License: CC BY Also in: fr

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The essentials

Quadruple-peaked emission around white dwarf WD J1328–1450 reveals two compositionally distinct gas rings, which the authors propose are sustained by two embedded planetesimals.

Question

What produces the unusual quadruple-peaked emission lines around WD J1328–1450, and what does this structure imply about gas generation and surviving planetary bodies in white dwarf debris discs?

Method

The authors combined VLT X-shooter spectroscopy obtained in 2021 and 2023 with survey photometry and Gaia parallax, deriving a white dwarf temperature of 17,424 ± 567 K and mass of 0.47 ± 0.09 solar masses. They fitted emission profiles using two concentric, coplanar circular gas discs with power-law surface brightness profiles, sampling the calcium-line model with Bayesian Markov chain Monte Carlo using 90 walkers. They also modelled the infrared excess using MCFOST radiative transfer and estimated planetesimal survival limits from tidal disruption constraints and assumed material strengths.

Findings

Result The calcium emission profiles imply gas rings extending approximately 0.14–0.34 and 0.54–1.93 solar radii from the white dwarf.
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From the derived posterior distributions shown in Supplementary Fig. 1, the radial extension of the inner gaseous disc goes from ~0.14 R⊙ to ~0.34 R⊙, while the outer disc extends from ~0.54 R⊙ to ~1.93 R⊙.
Result The nearly symmetric emission profiles remained unchanged for more than two years, supporting approximately circular, uniform gas discs.
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The nearly symmetric profile of the emission lines has remained unchanged for more than 2 years, supporting the hypothesis that the gas discs are close to circular and uniform.
Result The absence of detectable outer-ring magnesium emission indicates magnesium depletion relative to the inner ring.
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The complete absence of detectable Mg I emission from the outer disc therefore provides model-independent evidence that magnesium is significantly depleted in the outer disc relative to the inner disc.
Result The dust emits 2.7% of the stellar flux, placing this system among the brightest known dusty white dwarf debris discs.
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The fractional infrared flux excess of the dust disc around WD J1328–1450, that is, the ratio of the flux emitted by the disc and the stellar flux, is τ = 2.7%, making this one of the brightest dusty debris discs published to date1,9,10.
Authors’ interpretation The authors favor gas production through dust interactions with two planetesimals, one embedded within each ring.
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As the double-disc structure of WD J1328–1450 requires stable gas generation at two distinct and confined radial locations, we argue that dust interaction with a planetesimal analogous to SDSS J1228+1040 is the most likely origin of the gas, and two gas discs would therefore require two planetesimals on concentric orbits.

Limitations

The proposed planetesimals' exact orbits cannot be determined, although the gas-ring boundaries constrain their possible locations.
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Though we cannot determine the exact orbits of the two theorized planetesimals orbiting WD J1328–1450, the inner and outer edges of the two gas discs provide some stringent limits: the inner planetesimal must be located between 0.14 R⊙ and 0.34 R⊙ and the outer one between 0.54 R⊙ and 1.93 R⊙.
The infrared data do not uniquely constrain the dust configuration because multiple model parameters are degenerate.
See the passage in the paper
Although the model reproduces the observations, we note that several fit parameters are degenerate and alternative disc configurations may fit the data equally well.
Emission-line blending introduces difficult-to-quantify systematic uncertainties into the photospheric abundance measurements.
See the passage in the paper
The complexity of the underlying emission lines introduces systematic uncertainties that are difficult to quantify, and we stress that the uncertainties quoted in Extended Data Table 1 should be taken as estimates.

Why it matters

The authors argue that the stable double-ring system challenges existing gas-generation models and provides new constraints on debris-disc formation and evolution. It strengthens the hypothesis that interactions between dust and surviving planetesimals can sustain gaseous debris around white dwarfs.

Written by AI from the paper. Passages are checked word for word against the text we analysed; the rest may contain errors.

AI-generated keywords: White dwarf; Planetary debris discs; Circumstellar gas; Concentric gas rings; Planetesimals

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Original abstract

Gentile Fusillo and colleagues (2026) investigate the unusual debris surrounding the white dwarf WD J132800.85–145019.95, abbreviated WD J1328–1450. Planetary debris discs demonstrate that some planetary material survives its host star’s evolution into a white dwarf, but the mechanisms that produce and maintain gas within these discs remain uncertain. Unlike the 21 previously known gaseous-disc systems, which display double-peaked emission lines characteristic of rotating discs, WD J1328–1450 exhibits quadruple-peaked lines. The authors investigate the structure responsible for these profiles and how it can persist. The team identified the system through its infrared excess and obtained medium-resolution spectra using the X-shooter instrument on the Very Large Telescope in 2021 and 2023. They combined these observations with survey photometry and Gaia parallax measurements. Iterative stellar-atmosphere modelling yielded an effective temperature of 17,424 ± 567 K, a mass of 0.47 ± 0.09 solar masses, and a cooling age of approximately 73 million years. Calcium, magnesium, and silicon absorption lines confirm that the star is accreting planetary material, while emission from calcium, oxygen, magnesium, and iron traces circumstellar gas. The principal finding is that two concentric, coplanar, approximately circular gas rings reproduce the calcium emission profiles well. Using a Bayesian model of Keplerian rotation with power-law radial brightness distributions, the authors infer an inner ring extending from approximately 0.14 to 0.34 solar radii and an outer ring extending from 0.54 to 1.93 solar radii. The preferred inclination is 77 degrees, with uncertainties of +9 and −13 degrees. Oxygen emission supports this configuration, although line blending weakens the constraints. The profiles remained nearly unchanged for more than two years. Small intensity asymmetries could reflect non-uniform gas distributions, but there is no evidence of precession. Magnesium emission is detected only from the inner ring. The authors estimate that an outer-ring magnesium signal would have been detectable at approximately six standard deviations if both rings had the same calcium-to-magnesium ratio. They interpret its absence as evidence that the outer ring is magnesium-depleted relative to the inner ring. This compositional difference could indicate distinct parent bodies or different layers of a differentiated planetesimal. The star’s photospheric magnesium-to-silicon ratio is also unusually low, at approximately 0.2, although emission-line contamination makes this measurement uncertain. The dust emits approximately 2.7% of the star’s luminosity, placing WD J1328–1450 among the brightest known dusty white dwarfs. A vertically extended, moderately flared dust model reproduces the infrared excess with radial boundaries of 0.25 and 2 solar radii and a dust mass of 5 × 10^18 g. However, these parameters are highly degenerate, and the infrared data cannot establish whether the dust shares the gap between the gas rings. The authors favour a scenario in which two embedded planetesimals interact with dust to provide localized gas sources, while rapid recondensation limits gas spreading and preserves the gap. Tidal-survival calculations indicate that these bodies would require internal strength. Illustrative maximum diameters range from roughly 45–172 km within the inner ring to several thousand kilometres near the outer ring’s boundary, depending on composition and location. These values are model-dependent limits, not measured body sizes. Neither planetesimal has been directly detected. Alternatives such as self-shadowing are not conclusively excluded, although they lack established theoretical support. Overall, WD J1328–1450 provides strong evidence for two distinct gas-emitting regions and challenges existing models of white-dwarf debris-disc formation and evolution.

Two Rings of Planetary Wreckage Surround an Unusual White Dwarf

A dead star can still have a surprisingly active neighbourhood. Around some white dwarfs, the compact remnants of stars that have exhausted their nuclear fuel, shattered planetary material forms discs of dust and gas. These debris discs show that a star’s transformation into a white dwarf does not erase every trace of its planetary system.

But one white dwarf presents an especially intriguing puzzle. WD J132800.85–145019.95, shortened to WD J1328–1450, has gas emission unlike that of any previously known system of its kind. Rather than revealing one rotating gas disc, its light points to two distinct rings.

In their 2026 paper, “A double debris disc around a white dwarf sculpted by two planetary bodies,” N. P. Gentile Fusillo, Felipe Lagos-Vilches, Boris T. Gänsicke, Christopher J. Manser, and D. Koester investigate this unusual architecture—and how it might survive.

A Four-Peaked Clue

The key clue lies in the shapes of emission lines: bright features in a spectrum produced by gas. Rotating discs commonly generate double-peaked lines because gas on one side moves toward us while gas on the other moves away. Those motions shift the emitted light in opposite directions.

All 21 previously known white-dwarf systems with gaseous debris discs displayed these characteristic double peaks. WD J1328–1450 instead shows four peaks, suggesting a more complicated arrangement of emitting material.

The researchers identified the system through its infrared excess, a sign of surrounding warm dust. They then obtained medium-resolution spectra with the X-shooter instrument on the Very Large Telescope in 2021 and 2023, combining these observations with survey photometry and Gaia distance measurements.

Reading the Star and Its Rings

Iterative atmosphere modelling indicates that the white dwarf has a temperature of about 17,424 K, a mass of approximately 0.47 times the Sun’s mass, and a cooling age of roughly 73 million years. Absorption lines from calcium, magnesium, and silicon show that it is accreting planetary material. Meanwhile, emission from calcium, oxygen, magnesium, and iron reveals gas surrounding the star.

To explain the unusual calcium profiles, the team used a Bayesian model of gas moving in Keplerian orbits, where material closer to the star travels faster. Two concentric, coplanar, approximately circular rings reproduced the observations well:

The inner gas ring extends from approximately 0.14 to 0.34 solar radii.
The outer gas ring stretches from approximately 0.54 to 1.93 solar radii.
The preferred viewing inclination is 77 degrees, with uncertainties of +9 and −13 degrees.

Oxygen emission also supports this configuration, although overlapping spectral lines make its constraints weaker. Remarkably, the profiles remained nearly unchanged for more than two years. Small differences in peak intensity could reflect uneven gas distributions, but the observations show no evidence of precession—a gradual change in orbital orientation.

Different Rings, Different Ingredients?

The rings may differ chemically as well as spatially. Magnesium emission appears only in the inner ring. If both rings had the same calcium-to-magnesium ratio, the researchers estimate that magnesium from the outer ring should have been detectable at approximately six standard deviations.

Its absence therefore suggests that the outer ring is magnesium-depleted relative to the inner one. This could mean the rings originate from different parent bodies, or from different layers of a differentiated planetesimal—a body whose interior separated into chemically distinct regions.

The white dwarf’s atmosphere also appears to have an unusually low magnesium-to-silicon ratio of about 0.2. However, emission-line contamination makes that measurement uncertain, so it should not be treated as a definitive chemical fingerprint.

Bright Dust, Hidden Structure

The dust surrounding WD J1328–1450 emits approximately 2.7% of the star’s luminosity, placing it among the brightest known dusty white dwarfs. A vertically extended, moderately flared dust model can reproduce the infrared excess with boundaries at 0.25 and 2 solar radii and a dust mass of about 5 × 10^18 grams.

Those values are not unique, however: different combinations of model parameters can explain the data. Crucially, the infrared observations cannot establish whether the dust shares the gap separating the two gas rings.

Could Two Hidden Bodies Maintain the Rings?

The authors favour a scenario in which two embedded planetesimals interact with surrounding dust, providing localized sources of gas. Rapid recondensation could then limit the gas’s spread and preserve the gap.

Surviving so close to the white dwarf would require these bodies to possess internal strength. Model-dependent maximum diameters range from roughly 45–172 kilometres within the inner ring to several thousand kilometres near the outer ring’s boundary, depending on composition and location. These are illustrative limits, not measured sizes, and neither body has been directly detected.

Other explanations, including self-shadowing, remain possible, although they lack established theoretical support. The strongest conclusion is therefore not that two hidden bodies have been found, but that two distinct gas-emitting regions provide a compelling explanation for the observations. WD J1328–1450 offers a new challenge for understanding how planetary wreckage evolves around dead stars.

Created on 29 Oct. 2026

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A double debris disc around a white dwarf sculpted by two planetary bodies

The essentials

Question

Method

Findings

Limitations

Why it matters

Read further

Definitions

Two Rings of Planetary Wreckage Surround an Unusual White Dwarf

A Four-Peaked Clue

Reading the Star and Its Rings

Different Rings, Different Ingredients?

Bright Dust, Hidden Structure

Could Two Hidden Bodies Maintain the Rings?

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