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

Nicola Pietro Gentile Fusillo; Felipe Lagos-Vilches; Boris T. Gänsicke; Christopher J. Manser; Detlev Koester

doi:10.1038/s41550-026-03004-3

AI summary · arXiv: 2610.37773v1 · astro-ph.SR

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

Nicola Pietro Gentile Fusillo, Felipe Lagos-Vilches, Boris T. Gänsicke, Christopher J. Manser, Detlev Koester

Original paper · DOI 10.1038/s41550-026-03004-3 Submitted to arXiv on 27 Oct. 2026 42 pages, 9 figures, 5 tables, accepted for publication in Nature Astronomy License: CC BY 4.0 Also in: fr

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The essentials

Quadruple-peaked emission around white dwarf WD J1328−1450 reveals two stable, 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 concentric, coplanar circular gas discs with power-law brightness profiles and Bayesian MCMC sampling with 90 walkers. They also modelled the infrared excess using MCFOST radiative transfer and estimated planetesimal survival limits from tidal disruption and internal strength.

Findings

Result The nearly symmetric emission profiles remained unchanged for more than two years, supporting approximately circular, stable gas rings.
See the passage in the paper
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 calcium-line model places the inner ring at approximately 0.14–0.34 solar radii and the outer ring at approximately 0.54–1.93 solar radii.
See the passage in the paper
From the derived posterior distributions shown in Supplementary Fig. 1, the radial extension of the inner gaseous disc goes from $\approx 0.14$ to $\approx 0.34$ $R_{\odot}$, while the outer disc extends from $\approx 0.54$ to $\approx 1.93$ $R_{\odot}$.
Result The absence of outer-ring magnesium emission indicates magnesium depletion relative to the inner ring.
See the passage in the paper
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 fractional infrared excess is 2.7%, placing the system among the brightest known dusty white dwarf debris discs.
See the passage in the paper
The fractional infrared flux excess of the dust disc around WD J1328$-$1450, i.e. the ratio of the flux emitted by the disc and the stellar flux, is $\tau=2.7$ %, making this one of the brightest dusty debris disc published to date [13, 9, 10].
Authors’ interpretation The authors favour two embedded planetesimals interacting with dust as the mechanism sustaining gas generation at the two separate radial locations.
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Since the double disc structure about 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 from these observations.
See the passage in the paper
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 $R_{\odot}$ and 0.34 $R_{\odot}$ and outer one between 0.54 $R_{\odot}$ and 1.93 $R_{\odot}$.
The infrared dust model is non-unique because multiple fit 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.
Blended emission features introduce difficult-to-quantify systematic uncertainties into 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 stable double-ring configuration challenges gas-generation explanations based solely on inner-edge sublimation or collisional cascades and supplies new constraints on debris-disc evolution. The authors argue that it strengthens the case for surviving planetesimals generating gas through interactions with dust.

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 dwarfs; Circumstellar debris discs; Gaseous rings; Planetary remnants; Atmospheric pollution

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Comprehensive Summary
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Original abstract

This paper investigates the unusual debris surrounding the white dwarf WD J132800.85−145019.95, abbreviated WD J1328−1450, and explores what could produce and sustain two distinct gaseous rings around a stellar remnant. White dwarfs can accrete planetary material from circumstellar debris discs, some of which contain detectable gas. Unlike the double-peaked emission lines observed in the 21 previously published gaseous-disc systems, WD J1328−1450 exhibits four-peaked calcium and oxygen lines. The authors interpret these profiles as the superimposed signatures of two rotating rings and propose that two surviving planetary bodies generate the gas through interactions with dust. The system was initially identified by its excess infrared emission in survey photometry. The authors obtained medium-resolution spectra with the X-shooter instrument on the Very Large Telescope in 2021 and 2023, combining these observations with Gaia parallax measurements and optical and infrared photometry. An iterative fit of white dwarf atmosphere models to the spectroscopy and photometry 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 atmospheric pollution by planetary material, while emission from calcium, oxygen, magnesium, and iron reveals circumstellar gas. To reconstruct the emitting geometry, the authors fitted the line profiles with two concentric, coplanar, circular gas discs, each with a power-law radial brightness distribution. Bayesian modelling of the calcium triplet placed the inner ring between 0.14 and 0.34 solar radii and the outer ring between 0.54 and 1.93 solar radii. The inferred inclination is 77 degrees, with uncertainties of approximately −13 and +9 degrees. Oxygen emission broadly supports this configuration, although line blending weakens its constraints. The profiles remained essentially unchanged over two years, suggesting a stable, nearly circular arrangement. Small intensity asymmetries could reflect an uneven or clumpy gas distribution rather than orbital eccentricity. Magnesium emission is detected only from the inner ring. The authors estimate that an outer ring with the same calcium-to-magnesium ratio would produce magnesium peaks detectable at roughly six-sigma significance. They interpret the absence of these peaks as evidence of magnesium depletion in the outer ring, potentially indicating distinct parent bodies or different layers of a differentiated object. The dust produces a strong infrared excess equivalent to 2.7% of the stellar luminosity. A vertically extended, moderately flared dust model spanning approximately 0.25–2 solar radii can reproduce this emission. A conventional flat, opaque disc cannot simultaneously account for the infrared brightness and the inclination inferred from the gas. The preferred explanation involves two embedded planetesimals that supply gas locally through interactions with dust. Rapid recondensation would limit gas spreading and preserve the separation between the rings. Tidal-survival calculations indicate that the bodies require internal strength, particularly the inner body. Depending on orbital location and assumed material properties, the maximum permitted diameters range from approximately 45–172 km in the inner ring to several thousand kilometres near the outer ring’s boundary. These values are theoretical limits, not measured sizes. The discovery challenges simple gas-production models based solely on inner-edge sublimation or widespread collisional cascades. However, the proposed bodies have not been directly detected. The inferred gas geometry depends on modelling assumptions, dust parameters are highly degenerate, and emission-line blending complicates abundance measurements. Self-shadowing within a continuous disc remains a possible alternative to a physical gap in the gas. The observations therefore strongly support two separated emitting regions, while their origin and the underlying distribution of material remain uncertain.

Two Rings Around a Dead Star Hint at Surviving Planetary Bodies

A dead star can still host a surprisingly active planetary environment. Around the white dwarf WD J132800.85−145019.95, shortened to WD J1328−1450, astronomers have found evidence for two distinct regions of glowing gas amid dusty planetary debris. Their unusual arrangement raises a question: what keeps the gas separated rather than allowing it to spread into one continuous disc?

The paper “A double debris disc around a white dwarf sculpted by two planetary bodies,” by Nicola Pietro Gentile Fusillo, Felipe Lagos-Vilches, Boris T. Gänsicke, Christopher J. Manser, and Detlev Koester, proposes an intriguing answer. Two surviving planetesimals may be interacting with the surrounding dust, producing gas locally and maintaining the two emitting rings. The evidence for separate emitting regions is strong, but the proposed bodies remain unseen.

A Stellar Remnant with a Planetary Afterlife

White dwarfs are the compact remnants left behind after stars exhaust their nuclear fuel. Planetary material can survive this transformation, only to be disrupted later and form circumstellar debris discs. Some of that debris eventually falls onto the white dwarf, leaving detectable traces of heavy elements in its atmosphere.

WD J1328−1450 first attracted attention because survey measurements showed excess infrared radiation, a sign of warm dust. The researchers followed up with medium-resolution spectra taken using the X-shooter instrument on the Very Large Telescope in 2021 and 2023. They combined these observations with Gaia parallax measurements and optical and infrared photometry.

Their modelling places the white dwarf’s temperature at 17,424 ± 567 K and its mass at 0.47 ± 0.09 times the Sun’s mass. It has been cooling as a white dwarf for approximately 73 million years. Calcium, magnesium, and silicon absorption lines reveal atmospheric pollution by planetary material, while emission from calcium, oxygen, magnesium, and iron identifies gas around the star.

Why Four Peaks Matter

The striking discovery lies in the shapes of the emission lines. In the 21 previously published gaseous-disc systems, these lines showed two peaks. Such profiles arise naturally from rotating gas: material on one side moves toward us, while material on the other side moves away.

WD J1328−1450 instead displays four-peaked calcium and oxygen lines. The researchers interpret these as two overlapping pairs of peaks, produced by two rotating rings with different orbital speeds.

Mapping the Emitting Regions

To test that interpretation, the team modelled two concentric, coplanar, circular gas discs, allowing their brightness to vary with distance from the star. Bayesian modelling of the calcium triplet yielded the following configuration:

The inner emitting ring extends from approximately 0.14 to 0.34 solar radii.
The outer emitting ring spans approximately 0.54 to 1.93 solar radii.
The rings are viewed at an inclination of about 77 degrees, making the system nearly edge-on.

Oxygen emission broadly supports this geometry, although blended lines make its constraints less precise. The profiles also remained essentially unchanged over two years, consistent with a stable, nearly circular arrangement. Small differences in peak intensity could reflect clumpy or unevenly distributed gas rather than eccentric orbits.

A Chemical Difference Between the Rings

Magnesium offers another clue: its emission appears only in the inner ring. If the outer ring had the same calcium-to-magnesium ratio, the researchers estimate that its magnesium peaks would have been detectable at roughly six-sigma significance.

The missing peaks therefore suggest magnesium depletion in the outer emitting region. This could indicate two chemically different parent bodies, or material originating in different layers of a differentiated object. It is an intriguing possibility, not a definitive reconstruction of the system’s history, particularly because line blending complicates abundance measurements.

Dust, Hidden Bodies, and Local Gas Production

The dust is unusually prominent, radiating an infrared excess equivalent to 2.7% of the white dwarf’s luminosity. A conventional flat, opaque dust disc cannot simultaneously explain that brightness and the inclination inferred from the gas.

A vertically extended, moderately flared dust distribution spanning roughly 0.25–2 solar radii can reproduce the observations. Within this dusty environment, the authors propose that two embedded planetesimals generate gas through interactions with dust. Rapid recondensation could then prevent that gas from spreading far, preserving two separate emitting regions.

Surviving so close to the white dwarf would require internal strength, especially for the inner body. Depending on location and material properties, the calculated maximum permitted diameters range from about 45–172 kilometres in the inner ring to several thousand kilometres near the outer ring’s boundary. These are theoretical survival limits, not measured sizes.

A Compelling Picture, Not a Closed Case

The discovery challenges simple explanations based only on sublimation at a dust disc’s inner edge or widespread collisions. Yet important uncertainties remain. The inferred geometry depends on modelling assumptions, and several different dust configurations may fit the available data. Self-shadowing within a continuous disc could also create separated bright regions without requiring a physical gap in the gas.

WD J1328−1450 therefore offers compelling evidence for two separated emitting regions—not direct proof of two surviving bodies. Its unusual spectrum opens a window onto how planetary remnants may continue shaping their surroundings long after their star’s active life has ended.

Created on 02 Nov. 2026

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Weekly letter Presented in "Astronomy and space this week" of 2 November 2026. Astronomy and space this week: Hidden worlds, stellar futures and the temperature of uncertainty

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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 Around a Dead Star Hint at Surviving Planetary Bodies

A Stellar Remnant with a Planetary Afterlife

Why Four Peaks Matter

Mapping the Emitting Regions

A Chemical Difference Between the Rings

Dust, Hidden Bodies, and Local Gas Production

A Compelling Picture, Not a Closed Case

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