Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

A recurrent nova super-remnant in the Andromeda galaxy


The accretion of hydrogen onto a white dwarf star ignites a classical nova eruption1,2—a thermonuclear runaway in the accumulated envelope of gas, leading to luminosities up to a million times that of the Sun and a high-velocity mass ejection that produces a remnant shell (mainly consisting of insterstellar medium). Close to the upper mass limit of a white dwarf3 (1.4 solar masses), rapid accretion of hydrogen (about 10−7 solar masses per year) from a stellar companion leads to frequent eruptions on timescales of years4,5 to decades6. Such binary systems are known as recurrent novae. The ejecta of recurrent novae, initially moving at velocities of up to 10,000 kilometres per second7, must ‘sweep up’ the surrounding interstellar medium, creating cavities in space around the nova binary. No remnant larger than one parsec across from any single classical or recurrent nova eruption is known8,9,10, but thousands of successive recurrent nova eruptions should be capable of generating shells hundreds of parsecs across. Here we report that the most frequently recurring nova, M31N 2008-12a in the Andromeda galaxy (Messier 31 or NGC 224), which erupts annually11, is indeed surrounded by such a super-remnant with a projected size of at least 134 by 90 parsecs. Larger than almost all known remnants of even supernova explosions12, the existence of this shell demonstrates that the nova M31N 2008-12a has erupted with high frequency for millions of years.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Fig. 1: 12a and its surrounding super-remnant.
Fig. 2: Spectroscopy of the super-remnant shell.
Fig. 3: Results of hydrodynamic simulations of the interacting ejecta of multiple recurrent nova eruptions.

Data availability

All relevant data generated or analysed during this study are available from the corresponding author on reasonable request.


  1. Starrfield, S., Truran, J. W., Sparks, W. M. & Kutter, G. S. CNO abundances and hydrodynamic models of the nova outburst. Astrophys. J. 176, 169–176 (1972).

    Article  ADS  CAS  Google Scholar 

  2. Prialnik, D., Shara, M. M. & Shaviv, G. The evolution of a slow nova model with a Z = 0.03 envelope from pre-explosion to extinction. Astron. Astrophys. 62, 339–348 (1978).

    ADS  CAS  Google Scholar 

  3. Chandrasekhar, S. The maximum mass of ideal white dwarfs. Astrophys. J. 74, 81–82 (1931).

    Article  ADS  Google Scholar 

  4. Kato, M., Saio, H., Hachisu, I. & Nomoto, K. Shortest recurrence periods of novae. Astrophys. J. 793, 136 (2014).

    Article  ADS  Google Scholar 

  5. Hillman, Y., Prialnik, D., Kovetz, A. & Shara, M. M. Growing white dwarfs to the Chandrasekhar limit: the parameter space of the single degenerate SN Ia channel. Astrophys. J. 819, 168 (2016).

    Article  ADS  Google Scholar 

  6. Schaefer, B. Comprehensive photometric histories of all known Galactic recurrent novae. Astrophys. J. Suppl. Ser. 187, 275–373 (2010).

    Article  ADS  CAS  Google Scholar 

  7. Munari, U. et al. The 1999 outburst of the eclipsing and recurrent nova U Scorpii. Astron. Astrophys. 347, L39–L42 (1999).

    ADS  CAS  Google Scholar 

  8. Bode, M. F., O’Brien, T. J. & Simpson, M. Echoes of an explosive past: solving the mystery of the first superluminal source. Astrophys. J. 600, L63–L66 (2004).

    Article  ADS  CAS  Google Scholar 

  9. Shara, M. M., Martin, C. D., Seibert, M., Rich, R. M. & Salim, S. An ancient nova shell around the dwarf nova Z Camelopardalis. Nature 446, 159–162 (2007).

    Article  ADS  CAS  Google Scholar 

  10. Shara, M. M. et al. AT Cnc: a second dwarf nova with a classical nova shell. Astrophys. J. 758, 121 (2012).

    Article  ADS  Google Scholar 

  11. Darnley, M. J. et al. M31N 2008-12a—the remarkable recurrent nova in M31: panchromatic observations of the 2015 eruption. Astrophys. J. 833, 149 (2016).

    Article  ADS  Google Scholar 

  12. Stil, J. M. & Irwin, J. A. GSH 138-01-94: an old supernova remnant in the far outer Galaxy. Astrophys. J. 563, 816–827 (2001).

    Article  ADS  CAS  Google Scholar 

  13. Henze, M. et al. Breaking the habit—the peculiar 2016 eruption of the unique recurrent nova M31N 2008-12a. Astrophys. J. 857, 68 (2018).

    Article  ADS  Google Scholar 

  14. Kato, M., Saio, H. & Hachisu, I. Multi-wavelength light curve model of the one year recurrence period nova M31N 2008–12a. Astrophys. J. 808, 52 (2015).

    Article  ADS  Google Scholar 

  15. Darnley, M. J. et al. Inflows, outflows, and a giant donor in the remarkable recurrent nova M31N 2008-12a?—Hubble Space Telescope photometry of the 2015 eruption. Astrophys. J. 849, 96 (2017).

    Article  ADS  Google Scholar 

  16. Darnley, M. J. et al. No neon, but jets in the remarkable recurrent nova M31N 2008-12a?—Hubble Space Telescope spectroscopy of the 2015 eruption. Astrophys. J. 847, 35 (2017).

    Article  ADS  Google Scholar 

  17. Toonen, S., Voss, R. & Knigge, C. The influence of mass-transfer variability on the growth of white dwarfs, and the implications for type Ia supernova rates. Mon. Not. R. Astron. Soc. 441, 354–363 (2014).

    Article  ADS  Google Scholar 

  18. Ritossa, C., García-Berro, E. & Iben, I. On the evolution of stars that form electron-degenerate cores processed by carbon burning. II. Isotope abundances and thermal pulses in a 10 M ʘ model with an ONe core and applications to long-period variables, classical novae, and accretion-induced collapse. Astrophys. J. 460, 489–505 (1996).

    Article  ADS  CAS  Google Scholar 

  19. Darnley, M. J. et al. A remarkable recurrent nova in M31: discovery and optical/UV observations of the predicted 2014 eruption. Astron. Astrophys. 580, A45 (2015).

    Article  Google Scholar 

  20. Walterbos, R. A. M. & Braun, R. The interstellar medium of M31: III. Narrow-band imagery in Hα and [SΙΙ]. Astron. Astrophys. Suppl. Ser. 92, 625–682 (1992).

    ADS  CAS  Google Scholar 

  21. Shara, M. M., Zurek, D. R, Williams, R. E., Prialnik, D., Gilmozzi, R. & Moffat, A. F. J. HST imagery of the non-expanding, clumped “shell” of the recurrent nova T Pyxidis. Astron. J. 114, 258–275 (1997).

    Article  ADS  Google Scholar 

  22. Toraskar, J., Mac Low, M.-M., Shara, M. M. & Zurek, D. R. Dynamical fragmentation of the T Pyxidis nova shell during recurrent eruptions. Astrophys. J. 768, 48 (2013).

    Article  ADS  Google Scholar 

  23. Osterbrock, D. E. & Ferland, G. J. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei 2nd edn (University Science Books, Sausalito, 2006).

    Google Scholar 

  24. Kniazev, A. Y., Pustilnik, S. A. & Zucker, D. B. Spectroscopy of two PN candidates in IC10. Mon. Not. R. Astron. Soc. 384, 1045–1052 (2008).

    Article  ADS  CAS  Google Scholar 

  25. Sasaki, M., Pietsch, W., Haberl, F., Hatzidimitriou, D. & Stiele, H. Supernova remnants and candidates detected in the XMM-Newton M31 large survey. Astron. Astrophys. 544, A144 (2012).

    Article  ADS  Google Scholar 

  26. Long, K. S., Blair, W. P., Kirshner, R. P. & Winkler, P. F. An atlas of confirmed and candidate supernova remnants in M33. Astrophys. J. Suppl. Ser. 72, 61–73 (1990).

    Article  ADS  CAS  Google Scholar 

  27. Braun, R. & Walterbos, R. A. M. An atlas of supernova remnant candidates in Messier 31. Astron. Astrophys. Suppl. Ser. 98, 327–364 (1993).

    ADS  CAS  Google Scholar 

  28. Reynolds, R. J. & Tufte, S. L. A search for the He I λ5876 recombination line from the diffuse interstellar medium. Astrophys. J. 439, L17–L20 (1995).

    Article  ADS  CAS  Google Scholar 

  29. Whelan, J. & Iben, I. Binaries and supernovae of type I. Astrophys. J. 186, 1007–1014 (1973).

    Article  ADS  CAS  Google Scholar 

  30. Gutiérrez, J. et al. The final evolution of ONeMg electron-degenerate cores. Astrophys. J. 459, 701–705 (1996).

    Article  ADS  Google Scholar 

  31. Darnley, M. J. et al. A remarkable recurrent nova in M31: the optical observations. Astron. Astrophys. 563, L9 (2014).

    Article  ADS  Google Scholar 

  32. Henze, M. et al. A remarkable recurrent nova in M31: the X-ray observations. Astron. Astrophys. 563, L8 (2014).

    Article  ADS  Google Scholar 

  33. Henze, M. et al. A remarkable recurrent nova in M31: the 2010 eruption recovered and evidence of a six-month period. Astron. Astrophys. 582, L8 (2015).

    Article  ADS  Google Scholar 

  34. Shafter, A. W. et al. Recurrent novae in M31. Astrophys. J. Suppl. Ser. 216, 34 (2015).

    Article  ADS  Google Scholar 

  35. Steele, I. A., Smith, R. J., Rees, P. C., Barker, I. P. & Bates, S. D. The Liverpool Telescope: performance and first results. Proc. SPIE 5489, 679–692 (2004).

    Article  ADS  Google Scholar 

  36. Tody, D. in Astronomical Data Analysis Software and Systems II 173–183 (ASP, San Francisco, 1993).

  37. Stetson, P. B. DAOPHOT—a computer program for crowded-field stellar photometry. Publ. Astron. Soc. Pacif. 99, 191–222 (1987).

    Article  ADS  Google Scholar 

  38. Dressel, L. Wide Field Camera 3 Instrument Handbook Version 9.0 (STScI, Baltimore, 2017).

    Google Scholar 

  39. Fruchter, A. S., Hack, W., Dencheva, N., Droettboom, M. & Greenfield, P. BetaDrizzle: A Redesign of the MultiDrizzle Package. In STSCI Calibration Workshop Proceedings (eds Deustua, S. & Oliveira, C.) 376–381 (STScI, Baltimore, 2010).

  40. Currie, M. J. et al. in Astronomical Data Analysis Software and Systems XXIII 391–394 (ASP, San Francisco, 2014).

  41. Chonis, T. S., Hill, G. J., Lee, H., Tuttle, S. E. & Vattiat, B. L. LRS2: design, assembly, testing, and commissioning of the second-generation low-resolution spectrograph for the Hobby-Eberly Telescope. Proc. SPIE 99084, 1–28 (2016).

    Google Scholar 

  42. Davis, B. D., Ciardullo, R., Jacoby, G. H., Feldmeier, J. J. & Indahl, B. L. The true luminosities of planetary nebulae in M31's bulge: massive central stars from an old stellar population. Astrophys. J. 863, 189 (2018).

    Article  ADS  Google Scholar 

  43. Hamuy, M. et al. Southern spectrophotometric standards. Publ. Astron. Soc. Pacif. 104, 533–552 (1992).

    Article  ADS  Google Scholar 

  44. Slavin, A. J., O’Brien, T. J. & Dunlop, J. S. A deep optical imaging study of the nebular remnants of classical novae. Mon. Not. R. Astron. Soc. 276, 353–371 (1995).

    Article  ADS  Google Scholar 

  45. Freedman, W. L. & Madore, B. F. An empirical test for the metallicity sensitivity of the Cepheid period-luminosity relation. Astrophys. J. 365, 186–194 (1990).

    Article  ADS  Google Scholar 

  46. Vaytet, N. M. H., O’Brien, T. J. & Bode, M. F. Swift observations of the 2016 outburst of the recurrent nova RS Ophiuchi. II. One-dimensional hydrodynamical models of wind-driven shocks. Astrophys. J. 665, 654–662 (2007).

    Article  ADS  Google Scholar 

  47. Lloyd, H. M., O’Brien, T. J. & Bode, M. F. Shaping of nova remnants by binary motion. Mon. Not. R. Astron. Soc. 284, 137–147 (1997).

    Article  ADS  Google Scholar 

  48. Wareing, C. J. et al. The shaping of planetary nebula Sh 2—through interaction with the interstellar medium. Mon. Not. R. Astron. Soc. 366, 387–396 (2006).

    Article  ADS  CAS  Google Scholar 

  49. Bode, M. F. & Kahn, F. D. A model for the outburst of nova RS Ophiuchi in 1985. Mon. Not. R. Astron. Soc. 217, 205–215 (1985).

    Article  ADS  CAS  Google Scholar 

  50. Brandt, J. C., Stecher, T. P., Crawford, D. L. & Maran, S. P. The Gum nebula: fossil Strömgren sphere of the Vela X supernova. Astrophys. J. 163, L99–L104 (1971).

    Article  ADS  Google Scholar 

  51. Merrifield, M. R. The rotation curve of the Milky Way to 2.5R0 from the thickness of the H I layer. Astron. J. 103, 1552–1563 (1992).

    Article  ADS  CAS  Google Scholar 

  52. Jakobsen, P. et al. First results from the Faint Object Camera: SN 1987A. Astrophys. J. 369, L63–L66 (1991).

    Article  ADS  CAS  Google Scholar 

  53. Panagia, N., Gilmozzi, R., Macchetto, F., Adorf, H.-M. & Kirshner, R. P. Properties of the SN 1987A circumstellar ring and the distance to the Large Magellanic Cloud. Astrophys. J. 380, L23–L26 (1991).

    Article  ADS  CAS  Google Scholar 

  54. Massey, P. et al. A survey of local group galaxies currently forming stars. III. A search for luminous blue variables and other Hα emission-line stars. Astron. J. 134, 2474–2503 (2007).

    Article  ADS  CAS  Google Scholar 

  55. Vaytet, N. M. H. Numerical Modelling of the 2006 Outburst of RS Ophiuchi.  PhD thesis, Univ. Manchester, (2009).

  56. Vaytet, N. M. H. et al. Swift observations of the 2006 outburst of the recurrent nova RS Ophiuchi. III. X-ray spectral modeling. Astrophys. J. 740, 5 (2011).

    Article  ADS  Google Scholar 

  57. Dorman, B. & Arnaud, K. A. Redesign and reimplementation of XSPEC 2001 in astronomical data analysis software and systems X. ASP Conf. Proc. 238 415 (2001).

  58. Kato, M., Saio, H. & Hachisu, I. A millennium-long evolution of the 1 yr recurrent period nova—search for any indication of the forthcoming He flash. Astrophys. J. 844, 143 (2017).

    Article  ADS  Google Scholar 

  59. Kraft, R. P., Burrows, D. N. & Nousek, J. A. Determination of confidence limits for experiments with low numbers of counts. Astrophys. J. 374, 344–355 (1991).

    Article  ADS  Google Scholar 

Download references


The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias with financial support from the Science and Technology Facilities Council (STFC). This work is based on observations made with the NASA/ESA HST, obtained from the Data Archive at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA) under NASA contract NAS 5-26555. These observations are associated with programmes GO:14125 and GO:14651 for which financial support for R.H., M.H., M.M.S. and A.W.S. was provided by NASA through grants from STScI. This work is based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma. The Hobby–Eberly Telescope (HET) is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen. HET is named in honour of its principal benefactors, William P. Hobby and Robert E. Eberly. We thank Z. Levay for creating a colour composite image of the nova super-remnant, I. A. Steele for assistance with the Liverpool Telescope spectra, K. L. Page for assistance with XSPEC, K. A. Misselt and D. Baer for assistance with the Steward 2.3-m observations, also M. Link and C. Proffitt, and W. Eck and K. Long, the programme coordinators and contact scientists for HST GO:14125 and GO:14651, respectively. M.J.D. and M.W.H. acknowledge financial support and a PhD studentship, respectively, from the STFC. N.M.H.V. acknowledges support from the European Commission through the Horizon 2020 Marie Sklodowska-Curie Actions Individual Fellowship 2014 programme (grant agreement number 659706). V.A.R.M.R. acknowledges financial support from the Fundação para a Ciência e a Tecnologia in the form of an exploratory project (reference IF/00498/2015), from the Center for Research and Development in Mathematics and Applications (strategic project UID/MAT/04106/2013), and from Enabling Green E-science for the Square Kilometer Array Research Infrastructure (ENGAGE SKA), POCI-01-0145-FEDER- 022217, funded by Programa Operacional Competitividade e Internacionalização (COMPETE 2020) and the Fundação para a Ciência e a Tecnologia, Portugal.

Reviewer information

Nature thanks S. Shore and J. Sokoloski for their contribution to the peer review of this work.

Author information

Authors and Affiliations



All authors contributed to the discussion, proposing and planning of observations, data interpretation and writing of this manuscript. M.J.D. and S.C.W. led the Liverpool Telescope observations. M.J.D. and R.H. wrote the proposals and led the HST observations and resulting analysis. P.R.-G. and M.J.D. proposed and led the GTC observations and R.G.-R. assisted with their analysis. R.C. and B.D.D. obtained the HET spectrum. A.W.S. acquired the Steward 2.3-m Bok Telescope data. M.H. analysed the archival X-ray data. M.J.D., M.W.H. and S.C.W. undertook the photoionization analysis. M.J.D., T.J.O’B. and N.M.H.V. led the hydrodynamic simulations. M.J.D. and N.M.H.V. produced the synthetic X-ray spectra.

Corresponding author

Correspondence to M. J. Darnley.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 Additional multi-wavelength imaging of the super-remnant region.

a, The Steward 2.3-m Bok Telescope Hα image that allowed the association between the nebulosity and 12a to be made. Image orientation is as in Fig. 1 but the image is 80″ × 80″. bd, HST Wide Field Camera 3 broad-band filter images of the region around 12a. Image sizes are 40″ × 40″. These three panels show the F275W (ultraviolet) (b), F475W (optical) (c), and F814W (optical) (d) filters. The white contours in c show iso-flux regions as derived from the ground-based Hα + [N ii] image. As bd were taken towards the end of the 2015 eruption, the nova can be seen in the images. The F275W image clearly illustrates the lack of bright ultraviolet sources within the super-remnant. The white dashed ellipse indicates the extent of the super-remnant; the red dotted lines indicate the position of 12a.

Extended Data Fig. 2 HET flux-calibrated spectrum of the super-remnant outer-shell.

As with the GTC spectrum of the same region (Fig. 2), there is negligible continuum and hydrogen Balmer emission lines and nebular lines of [N ii], [O ii] and [S ii]. The mean spectral resolution for the ‘blue arm’ is 1.68 Å and for the ‘orange arm’ is 4.04 Å (see Methods). Gaps in the spectrum indicate areas where skyline subtraction residuals remained.

Extended Data Fig. 3 Comparison of results from the hydrodynamic modelling using a range of spatial resolutions.

The blue and green lines indicate simulations of 20 eruptions with spatial resolutions of 0.02 au and 0.2 au, respectively, while the red and black lines indicate simulations of 100 eruptions with resolution 0.2 au and 0.4 au, respectively. a, Gas density radial distribution; the lower black dotted horizontal line indicates the ISM density, with the upper dotted line showing the consistent peak density of the super-remnant shell. b, Gas pressure radial distribution. c, Gas velocity radial distribution. d, Gas temperature radial distribution.

Extended Data Fig. 4 The effect of radiative cooling on the super-remnant dynamics.

ad, Panels as in Extended Data Fig. 3. The close match between the results of simulations of 1,000 eruptions without radiative cooling (black) and with radiative cooling (blue).

Extended Data Fig. 5 Additional results of the hydrodynamic simulations of the interacting ejecta of multiple recurrent nova eruptions.

a, The mass growth of the super-remnant outer shell for up to 100,000 eruptions (see key). The diagonal dotted line illustrates a power-law extrapolation of the outer-shell mass to further eruptions. The upper and lower solid grey lines indicate the growth of the outer-shell mass for higher and lower ISM densities, respectively. The horizontal dotted line marks the predicted outer-shell mass at the current extent of the super-remnant. b, The evolution of the expansion velocity of the outer shell (black) compared to the mean velocity within the ejecta pile-up region (red). The diagonal dotted lines indicate power-law extrapolations, the horizontal line the initial injection velocity, and the vertical line the predicted current epoch. c, The evolution of the X-ray (0.3–10 keV) luminosity of the super-remnant (black), the hard (1–10 keV; red) and soft (0.3–1 keV; blue) components are shown for information along with the hardness ratio HR (hard/soft; right-hand axis) evolution; for each, the dotted line indicates a power-law extrapolation to later times. The horizontal dotted black line indicates the 3σ upper limit from the XMM-Newton observations.

Extended Data Fig. 6 The full (uncooled) simulations of 100,000 eruptions.

ad, Panels as in Extended Data Fig. 4.

Extended Data Fig. 7 Super-remnant X-ray emission modelling.

In both panels the cyan, blue, green, red and black lines indicate simulations of 10, 100, 1,000, 10,000 and 100,000 eruptions, respectively. The top panel shows the contribution to the super-remnant emission as a function of photon energy (in units of kT). The vertical dotted line indicates the lower-limit (0.08 keV) cut-off for input into XSPEC. The bottom panel shows the resultant synthetic X-ray spectra of the super-remnant (0.3–10 keV).

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Darnley, M.J., Hounsell, R., O’Brien, T.J. et al. A recurrent nova super-remnant in the Andromeda galaxy. Nature 565, 460–463 (2019).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing