The detection1 of a dust disk around the white dwarf star G29-38 and transits from debris orbiting the white dwarf WD 1145+017 (ref. 2) confirmed that the photospheric trace metals found in many white dwarfs3 arise from the accretion of tidally disrupted planetesimals4. The composition of these planetesimals is similar to that of rocky bodies in the inner Solar System5. Gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies6, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a hot (about 27,750 kelvin) white dwarf, WD J091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3 × 109 grams per second. The composition of this disk is unlike all other known planetary debris around white dwarfs7, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H2O and H2S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. The orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of approximately 1 in 10,000 for spectroscopically detectable giant planets in close orbits around white dwarfs.
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Cloudy is publicly available (https://www.nublado.org/). The model atmosphere code of D. Koester is subject to restricted availability.
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Funding for the Sloan Digital Sky Survey IV was provided by the Alfred P. Sloan Foundation, the US Department of Energy Office of Science, and the Participating Institutions. The SDSS website is www.sdss.org. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0102.C-0351(A). B.T.G. and C.J.M. were supported by the UK STFC grant ST/P000495. M.R.S. acknowledges support from the Millennium Nucleus for Planet Formation (NPF) and Fondecyt (grant 1181404). O.T. was supported by a Leverhulme Trust Research Project Grant. The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme number 677706 (WD3D).
The authors declare no competing interests.
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Extended data figures and tables
The unusual nature of WD J0914+1914 was identified from its optical spectrum within SDSS Data Release 14. The Hα, O i 7,774 Å and O i 8,446 Å lines are clearly detected, S [ii] 4,068 Å and a blend of S i and O i near 9,240 Å are present near the noise level.
The double-peaked emission lines of hydrogen (a), oxygen (b, c, e, f) and sulfur (d) detected in the optical spectrum of WD J0914+1914 originate in a gaseous circumstellar disk. Shown in red are synthetic disk profiles computed by convolving the Cloudy model that best matches the observed line flux ratios with the broadening function of a Keplerian disk. Adopting an inclination of i = 60°, the widths and double-peak separations of the Hα (a) and O i 8,446 Å (c) lines are well reproduced for inner and outer disk radii of rin ≈ (1.0–1.3)R⊙ and rout ≈ (2.8–3.3)R⊙, respectively, consistent with the results from the Cloudy models (see Extended Data Fig. 4). The emission of [S ii] 4,068 Å (d) extends from about 1R⊙ to 10R⊙. The V-shaped central depression of the O i 8,446 Å (c) line suggests that the line is optically thick.
Extended Data Fig. 3 Dynamical constraints on the location of the circumstellar gas emitting the observed double-peaked emission lines.
The gas in the circumstellar disk follows Keplerian orbits, and hence the profile shape of the observed emission lines (see Fig. 1 and Extended Data Fig. 2) encodes the location of the gas. The velocity separation of the double-peaks and the maximum velocity in the line wings correspond to motion of gas at the outer edge and inner edge of the disk, respectively. For a given inclination of the disk, these velocities map into semi-major axes. A lower limit on the inclination, i > 5°, arises from the finite size of the white dwarf (Rwd), and an upper limit on the extent of the disk is provided for an edge-on, i = 90°, inclination. The forbidden [S ii] 4,068 Å line has a much smaller separation of the double-peaks compared to Hα and O i 8,446 Å, implying a larger radial extent.
The line flux ratios of a grid of Cloudy models spanning a range of gas densities, ρ, and radial distances from the white dwarf, r, from the white dwarf are compared to the observed values. The two histograms show the average quality for constant r (top) and constant ρ (right). The observed emission line fluxes are reasonably well reproduced by photo-ionized gas with a density of ρ = 10−11.3 g cm−3 and located at about (1–4)R⊙.
a, Comparison of the irradiating EUV flux around T Tauri stars (yellow-shaded region) and that of WD J0914+1914 (red line). The outer border of the warm Neptune desert is indicated by the vertical dashed line. The orbital separation of the planet orbiting WD J0914+1914 estimated from the size of the accretion disk is about (14–16)R⊙ (grey-shaded region). Subject to an EUV luminosity comparable to that of planets around T Tauri stars, the giant planet at WD J0914+1914 is well within the warm Neptune desert. b, Mass loss rates estimated from the assumption of recombination and energy limited hydrodynamic escape for a Jupiter mass and a Neptune mass planet. Substantial mass loss could be generated even for separations of up to a few hundred solar radii, well beyond the estimated orbital location of the giant planet at WD J0914+1914.
a, Lyα irradiance of the Sun across a full solar activity cycle as measured by the SORCE SOLSTICE instrument. The radiation pressure on neutral interplanetary hydrogen in the solar system usually exceeds the gravitational force exerted by the Sun. b, The Lyα flux of the Sun during minimum (2008) and maximum (2014) in comparison to the emission of WD J0914+1914 at a distance of 15R⊙. Given that WD J0914+1914 is less massive than the Sun, and that its Lyα flux is comparable to that of the Sun in the core of the line, but much larger in the wings (even during the 2014 solar maximum), radiation pressure strongly impedes the inflow of hydrogen, explaining the large depletion of hydrogen with respect to oxygen and sulfur within the circumstellar disk.
Extended Data Fig. 7 Final separation after common envelope evolution as a function of planetary mass.
We adopted two common envelope efficiencies, α = 0.25 (solid line), and α = 1.0 (dashed line) to calculate an upper limit for the final separation (afinal) if the progenitor of WD J0914+1914 and the planet evolved through a common envelope phase. The parameter space of possible outcomes of common envelope evolution lies below these lines (grey-shaded region). We consider the smaller efficiency to be more realistic. For configurations below the red line (aphot), the planetary mass object will evaporate inside the giant envelope; below the blue line (aRL), it would overflow its Roche lobe. Only planets with parameters within the green-shaded region can survive common envelope evolution. Whereas common envelope evolution can bring a Jupiter-mass planet to the estimated location of the planet around WD J0914+1914 (at (14–16)R⊙), smaller planets will be evaporated in the giant envelope.
White dwarfs cool with time and as a consequence their EUV luminosity decreases. We calculated model spectra for effective temperatures from 80,000 K to 10,000 K, integrated the EUV flux, and determined the mass loss rate of a Jupiter and a Neptune at a distance of 10R⊙. At a cooling age of 364 million years the white dwarf will have cooled down to 12,000 K, the mass loss rate will drop below about 106 g s−1, and the resulting photospheric contamination by oxygen and sulfur will become undetectable. Integrating the mass loss rate over the entire cooling time results in a total mass loss of about 0.002MJup, which corresponds to about 3.7% of the mass of Neptune.
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Gänsicke, B.T., Schreiber, M.R., Toloza, O. et al. Accretion of a giant planet onto a white dwarf star. Nature 576, 61–64 (2019). https://doi.org/10.1038/s41586-019-1789-8
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