A massive white-dwarf merger product before final collapse

Abstract

Gravitational-wave emission can lead to the coalescence of close pairs of compact objects orbiting each other1,2. In the case of neutron stars, such mergers may yield masses above the Tolman–Oppenheimer–Volkoff limit (2 to 2.7 solar masses)3, leading to the formation of black holes4. For white dwarfs, the mass of the merger product may exceed the Chandrasekhar limit, leading either to a thermonuclear explosion as a type Ia supernova5,6 or to a collapse forming a neutron star7,8. The latter case is expected to result in a hydrogen- and helium-free circumstellar nebula and a hot, luminous, rapidly rotating and highly magnetized central star with a lifetime of about 10,000 years9,10. Here we report observations of a hot star with a spectrum dominated by emission lines, which is located at the centre of a circular mid-infrared nebula. The widths of the emission lines imply that wind material leaves the star with an outflow velocity of 16,000 kilometres per second and that rapid stellar rotation and a strong magnetic field aid the wind acceleration. Given that hydrogen and helium are probably absent from the star and nebula, we conclude that both objects formed recently from the merger of two massive white dwarfs. Our stellar-atmosphere and wind models indicate a stellar surface temperature of about 200,000 kelvin and a luminosity of about 104.6 solar luminosities. The properties of the star and nebula agree with models of the post-merger evolution of super-Chandrasekhar-mass white dwarfs9, which predict a bright optical and high-energy transient upon collapse of the star11 within the next few thousand years. Our observations indicate that super-Chandrasekhar-mass white-dwarf mergers can avoid thermonuclear explosion as type Ia supernovae, and provide evidence of the generation of magnetic fields in stellar mergers.

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Fig. 1: New mid-infrared nebula in Cassiopeia.
Fig. 2: Spectral modelling of J005311.
Fig. 3: Position of J005311 in the Hertzsprung–Russell diagram.

Data availability

All data and codes that support the findings of this study are available upon request from the corresponding co-authors.

References

  1. 1.

    Hulse, R. A. & Taylor, J. H. Discovery of a pulsar in a binary system. Astrophys. J. 195, L51–L53 (1975).

    ADS  Article  Google Scholar 

  2. 2.

    Abbott, B. P. et al. Observation of gravitational waves from a binary black hole merger. Phys. Rev. Lett. 116, 061102 (2016).

    ADS  MathSciNet  CAS  Article  Google Scholar 

  3. 3.

    Özel, F. & Freire, P. Masses, radii, and the equation of state of neutron stars. Annu. Rev. Astron. Astrophys. 54, 401–440 (2016).

  4. 4.

    Abbott, B. P. et al. Gravitational waves and gamma-rays from a binary neutron star merger: GW170817 and GRB 170817A. Astrophys. J. 848, L13 (2017).

    ADS  Article  Google Scholar 

  5. 5.

    Iben, I. & Tutukov, A. V. Supernovae of type I as end products of the evolution of binaries with components of moderate initial mass (M ≤ 9M ʘ). Astron. Astrophys. Suppl. Ser. 54, 335–372 (1984).

    ADS  CAS  Article  Google Scholar 

  6. 6.

    Pakmor, R. et al. Violent mergers of nearly equal-mass white dwarf as progenitors of subluminous Type Ia supernovae. Astron. Astrophys. 528, A117 (2011).

    Article  Google Scholar 

  7. 7.

    Saio, H. & Nomoto, K. Off-center carbon ignition in rapidly rotating, accreting carbon-oxygen white dwarfs. Astrophys. J. 615, 444–449 (2004).

    ADS  CAS  Article  Google Scholar 

  8. 8.

    Shen, K. J., Bildsten, L., Kasen, D. & Quataert, E. The long-term evolution of double white dwarf mergers. Astrophys. J. 748, 35 (2012).

    ADS  Article  Google Scholar 

  9. 9.

    Schwab, J., Quataert, E. & Kasen, D. The evolution and fate of super-Chandrasekhar mass white dwarf merger remnants. Mon. Not. R. Astron. Soc. 463, 3461–3475 (2016).

    ADS  CAS  Article  Google Scholar 

  10. 10.

    Ji, S. et al. The post-merger magnetized evolution of white dwarf binaries: the double-degenerate channel of sub-Chandrasekhar Type Ia supernovae and the formation of magnetized white dwarfs. Astrophys. J. 773, 136 (2013).

    ADS  Article  Google Scholar 

  11. 11.

    Dessart, L. et al. Multidimensional simulations of the accretion-induced collapse of white dwarfs to neutron stars. Astrophys. J. 644, 1063–1084 (2006).

    ADS  CAS  Article  Google Scholar 

  12. 12.

    Wright, E. L. et al. The Wide-field Infrared Survey Explorer (WISE): mission description and initial on-orbit performance. Astron. J. 140, 1868–1881 (2010).

    ADS  Article  Google Scholar 

  13. 13.

    Drew, J. E. et al. The INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS). Mon. Not. R. Astron. Soc. 362, 753–776 (2005).

    ADS  CAS  Article  Google Scholar 

  14. 14.

    Giammichele, N. et al. A large oxygen-dominated core from the seismic cartography of a pulsating white dwarf. Nature 554, 73–76 (2018).

    ADS  CAS  Article  Google Scholar 

  15. 15.

    Bailer-Jones, C. A. L., Rybizki, J., Fouesneau, M., Mantelet, G. & Andrae, R. Estimating distances from parallaxes IV: distances to 1.33 billion stars in Gaia Data Release 2. Astron. J. 156, 58 (2018).

    ADS  Article  Google Scholar 

  16. 16.

    Tramper, F. et al. Massive stars on the verge of exploding: the properties of oxygen sequence Wolf–Rayet stars. Astron. Astrophys. 581, A110 (2015).

    Article  Google Scholar 

  17. 17.

    Gesicki, K. et al. Planetary nebulae with emission-line central stars. Astron. Astrophys. 451, 925–935 (2006).

    ADS  CAS  Article  Google Scholar 

  18. 18.

    Dufour, P., Liebert, J., Fontaine, G. & Behara, N. White dwarf stars with carbon atmospheres. Nature 450, 522–524 (2007).

    ADS  CAS  Article  Google Scholar 

  19. 19.

    Werner, K. & Rauch, T. Analysis of HST/COS spectra of the bare C–O stellar core H1504+65 and a high-velocity twin in the Galactic halo. Astron. Astrophys. 584, A19 (2015).

    ADS  Article  Google Scholar 

  20. 20.

    Flagey, N., Noriega-Crespo, A., Billot, N. & Carey, S. J. Spitzer/infrared spectrograph investigation of MIPSGAL 24 μm compact bubbles. Astrophys. J. 741, 4 (2011).

    ADS  Article  Google Scholar 

  21. 21.

    Poe, C. H., Friend, D. B. & Cassinelli, J. P. A rotating, magnetic, radiation-driven wind model for Wolf–Rayet stars. Astrophys. J. 337, 888–902 (1989).

    ADS  Article  Google Scholar 

  22. 22.

    Petit, V. et al. A magnetic confinement versus rotation classification of massive-star magnetospheres. Mon. Not. R. Astron. Soc. 429, 398–422 (2013).

    ADS  CAS  Article  Google Scholar 

  23. 23.

    Beloborodov, A. M. Magnetically powered outbursts from white dwarf mergers. Mon. Not. R. Astron. Soc. 438, 169–176 (2014).

    ADS  Article  Google Scholar 

  24. 24.

    Wickramasinghe, D. T. & Ferrario, L. Magnetism in isolated and binary white dwarfs. Publ. Astron. Soc. Pacif. 112, 873–924 (2000).

    ADS  Article  Google Scholar 

  25. 25.

    de Mink, S. E., Sana, H., Langer, N., Izzard, R. G. & Schneider, F. R. N. The incidence of stellar mergers and mass gainers among massive stars. Astrophys. J. 782, 7 (2014).

    ADS  Article  Google Scholar 

  26. 26.

    Maoz, D., Hallakoun, N. & Badenes, C. The separation distribution and merger rate of double white dwarfs: improved constraints. Mon. Not. R. Astron. Soc. 476, 2584–2590 (2018).

    ADS  CAS  Article  Google Scholar 

  27. 27.

    Fossati, L. et al. Evidence of magnetic field decay in massive main-sequence stars. Astron. Astrophys. 592, A84 (2016).

    Article  Google Scholar 

  28. 28.

    Dar, A., Kozlovsky, B. Z., Nussinov, S. & Ramaty, R. Gamma-ray bursts and cosmic rays from accretion-induced collapse. Astrophys. J. 388, 164–170 (1992).

    ADS  CAS  Article  Google Scholar 

  29. 29.

    Gvaramadze, V. V., Kniazev, A. Y. & Fabrika, S. Revealing evolved massive stars with Spitzer. Mon. Not. R. Astron. Soc. 405, 1047–1060 (2010).

    ADS  Google Scholar 

  30. 30.

    Gvaramadze, V. V. et al. Discovery of two new Galactic candidate luminous blue variables with Wide-field Infrared Survey Explorer. Mon. Not. R. Astron. Soc. 421, 3325–3337 (2012).

    ADS  CAS  Article  Google Scholar 

  31. 31.

    Wenger, M. et al. The SIMBAD astronomical database. The CDS reference database for astronomical objects. Astron. Astrophys. 143, 9–22 (2000).

    ADS  Google Scholar 

  32. 32.

    Barentsen, G. et al. The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2). Mon. Not. R. Astron. Soc. 444, 3230–3257 (2014).

    ADS  CAS  Article  Google Scholar 

  33. 33.

    Afanasiev, V. L. & Moiseev, A. V. The SCORPIO universal focal reducer of the 6-m telescope. Astron. Lett. 31, 194–204 (2005).

    ADS  Article  Google Scholar 

  34. 34.

    Oke, J. B. Faint spectrophotometric standard stars. Astron. J. 99, 1621–1631 (1990).

    ADS  Article  Google Scholar 

  35. 35.

    Maryeva, O. & Abolmasov, P. ScoRe – Package for Long-Slit Spectroscopic Data Reduction; http://www.sao.ru/hq/ssl/maryeva/score.html.

  36. 36.

    Crowther, P. A., De Marco, O. & Barlow, M. J. Quantitative classification of WC and WO stars. Mon. Not. R. Astron. Soc. 296, 367–378 (1998).

    ADS  CAS  Article  Google Scholar 

  37. 37.

    Werner, K., Rauch, T. & Kruk, J. W. Identification of Ne VIII lines in H-deficient (pre-) white dwarfs: a new tool to constrain the temperature of the hottest stars. Astron. Astrophys. 474, 591–597 (2007).

    ADS  CAS  Article  Google Scholar 

  38. 38.

    Torres, A. V. & Massey, P. An atlas of optical spectrophotometry of Wolf-Rayet carbon and oxygen stars. Astrophys. J. Suppl. Ser. 65, 459–483 (1987).

    ADS  CAS  Article  Google Scholar 

  39. 39.

    Tramper, F. et al. On the nature of WO stars: a quantitative analysis of the WO3 star DR1 in IC 1613. Astron. Astrophys. 559, A72 (2013).

    Article  Google Scholar 

  40. 40.

    Koesterke, L., Hamann, W.-R. & Gräfener, G. Expanding atmospheres in non-LTE. Radiation transfer using short characteristics. Astron. Astrophys. 384, 562–567 (2002).

    ADS  Article  Google Scholar 

  41. 41.

    Gräfener, G., Koesterke, L. & Hamann, W.-R. Line-blanketed model atmospheres for WR stars. Astron. Astrophys. 387, 244–257 (2002).

    ADS  Article  Google Scholar 

  42. 42.

    Hamann, W.-R. & Gräfener, G. A temperature correction method for expanding atmospheres. Astron. Astrophys. 410, 993–1000 (2003).

    ADS  Article  Google Scholar 

  43. 43.

    Gräfener, G. & Hamann, W.-R. Hydrodynamic model atmospheres for WR stars. Self-consistent modeling of a WC star wind. Astron. Astrophys. 432, 633–645 (2005).

    ADS  Article  Google Scholar 

  44. 44.

    Cunto, W., Mendoza, C., Ochsenbein, F. & Zeippen, C. J. Topbase at the CDS. Astrophys. J. 275, L5–L8 (1993).

    ADS  CAS  Google Scholar 

  45. 45.

    Kramida, A. et al. NIST Atomic Spectra Database (v. 5.6.1) (National Institute of Standards and Technology, Gaithersburg, 2013); http://physics.nist.gov/asd.

  46. 46.

    Iglesias, C. A. & Rogers, F. J. Updated Opal opacities. Astrophys. J. 464, 943–953 (1996).

    ADS  CAS  Article  Google Scholar 

  47. 47.

    Cardelli, J. A., Clayton, G. C. & Mathis, J. S. The determination of ultraviolet extinction from the optical and near-infrared. Astrophys. J. 329, L33–L37 (1988).

    ADS  Article  Google Scholar 

  48. 48.

    Cutri, R. M. et al. 2MASS All-Sky Catalog of Point Sources VizieR Online Data Catalog 2246 (2003); http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=II/246.

  49. 49.

    Hamann, W.-R. & Koesterke, L. Spectrum formation in clumped stellar winds: consequences for the analyses of Wolf–Rayet spectra. Astron. Astrophys. 335, 1003–1008 (1998).

    ADS  CAS  Google Scholar 

  50. 50.

    Bestenlehner, J. M. et al. The VLT-FLAMES Tarantula Survey. XVII. Physical and wind properties of massive stars at the top of the main sequence. Astron. Astrophys. 570, A38 (2014).

    Article  Google Scholar 

  51. 51.

    Gräfener, G. & Vink, J. S. Stellar mass-loss near the Eddington limit. Tracing the sub-photospheric layers of classical Wolf–Rayet stars. Astron. Astrophys. 560, A6 (2013).

    ADS  Article  Google Scholar 

  52. 52.

    Gräfener, G., Owocki, S. P., Grassitelli, L. & Langer, N. On the optically thick winds of Wolf–Rayet stars. Astron. Astrophys. 608, A34 (2017).

    ADS  Article  Google Scholar 

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Acknowledgements

We thank T. Rauch and K. Werner for discussions and for providing atomic data through the Tübingen Model Atom Database in the framework of the German Virtual Observatory. V.V.G. acknowledges support from the Russian Science Foundation under grant 14-12-01096 and from the Russian Foundation for Basic Research (RFBR) under grant 19-02-00779. G.G. acknowledges financial support from Deutsche Forschunsgemeinschaft (DFG) under grant GR 1717/5-1. O.V.M. acknowledges support from RFBR under grant 16-02-00148 and from the Čzech Science Foundation under grant GA ČR 18-05665S. A.Y.K. acknowledges support from RFBR under grant 16-02-00148 and from the National Research Foundation (NRF) of South Africa. The TMAD tool (http://astro.uni-tuebingen.de/~TMAD) used in this study was constructed as part of the activities of the German Astrophysical Virtual Observatory. This research made use of the SIMBAD database, operated at CDS, Strasbourg, France.

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Contributions

V.V.G., G.G. and N.L. jointly analysed and interpreted observational data and wrote the manuscript. O.V.M. obtained and reduced the spectroscopic material. A.Y.K. provided ideas for the interpretation of the nebula. A.S.M. and O.I.S. obtained optical photometry data. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Vasilii V. Gvaramadze or Götz Gräfener.

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Extended data figures and tables

Extended Data Fig. 1 Neon features in our models.

Comparison of models with neon surface mass fractions of 0.0 (red), 0.1 (green) and 0.5 (blue) with observations (black). The observed and calculated fluxes are divided by the same modelled continuum flux fc.

Extended Data Fig. 2 Abundances.

a, Comparison of the observed spectrum of J005311 (black line) with our best-fitting model (helium mass fraction Y = 0.0; blue) with models with increased helium abundance (Y = 0.1, green; Y = 0.2, red). b, Comparison of our best-fitting model (carbon mass fraction X(C) = 0.2; blue) with models with altered carbon abundance (X(C) = 0.1, green; X(C) = 0.3, red).

Extended Data Fig. 3 Stellar temperature.

a, Comparison of our best-fitting model (211,000 K; black) with models that are hotter (266,000 K; red) and cooler (178,000 K; blue) than the temperature range given in Table 1. b, Magnified profiles of the O vi 4,500 Å and C iv 4,660 Å lines.

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Gvaramadze, V.V., Gräfener, G., Langer, N. et al. A massive white-dwarf merger product before final collapse. Nature 569, 684–687 (2019). https://doi.org/10.1038/s41586-019-1216-1

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