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.

  • Letter
  • Published:

An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae


Type Ia supernovae form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates1. This one-parameter behaviour allows type Ia supernovae to be calibrated as cosmological ‘standard candles’, and led to the discovery of an accelerating Universe2,3. Recent investigations, however, have revealed that the true nature of type Ia supernovae is more complicated. Theoretically, it has been suggested4,5,6,7,8 that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf progenitor, possibly as a result of convection before the explosion4. Observationally, the diversity seen in the spectral evolution of type Ia supernovae beyond the luminosity–decline-rate relation is an unresolved issue9,10. Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed. Our findings suggest that the spectral evolution diversity is no longer a concern when using type Ia supernovae as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre is a generic feature of type Ia supernovae.

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

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Comparison between HVG type Ia SN 2002bo and LVG type Ia SN 1998bu.
Figure 2: Relations between the features in early and late phases.
Figure 3: A schematic picture of the structure of type Ia supernovae ejecta.
Figure 4: Expectations from a hydrodynamic explosion model.

Similar content being viewed by others


  1. Phillips, M. M. et al. The reddening-free decline rate versus luminosity relationship for Type IA supernovae. Astron. J. 118, 1766–1776 (1999)

    Article  ADS  Google Scholar 

  2. Permutter, S. et al. Measurements of Ω and Λ from 42 high-redshift supernovae. Astrophys. J. 517, 565–586 (1999)

    Article  ADS  Google Scholar 

  3. Riess, A. et al. Observational evidence from supernovae for an accelerating universe and a cosmological constant. Astron. J. 116, 1009–1038 (1998)

    Article  ADS  Google Scholar 

  4. Kuhlen, M., Woosley, S. E. & Glatzmaier, G. A. Carbon ignition in type Ia supernovae. II. A three-dimensional numerical model. Astrophys. J. 640, 407–416 (2006)

    Article  ADS  CAS  Google Scholar 

  5. Kasen, D., Röpke, F. K. & Woosley, S. E. The diversity of type Ia supernovae from broken symmetries. Nature 460, 869–872 (2009)

    Article  ADS  CAS  Google Scholar 

  6. Maeda, K. et al. Nucleosynthesis in two-dimensional delayed detonation models of type Ia supernova explosions. Astrophys. J. 712, 624–638 (2010)

    Article  ADS  CAS  Google Scholar 

  7. Röpke, F. K., Woosley, S. E. & Hillebrandt, W. Off-center ignition in type Ia supernovae. I. Initial evolution and implications for delayed detonation. Astrophys. J. 660, 1344–1356 (2007)

    Article  ADS  Google Scholar 

  8. Jordan, G. C. et al. Three-dimensional simulations of the deflagration phase of the gravitationally confined detonation model of type Ia supernovae. Astrophys. J. 681, 1448–1457 (2008)

    Article  ADS  CAS  Google Scholar 

  9. Branch, D., Drucker, W. & Jeffery, D. J. Differences among expansion velocities of type Ia supernovae. Astrophys. J. 330, L117–L118 (1988)

    Article  ADS  CAS  Google Scholar 

  10. Benetti, S. et al. The diversity of type Ia supernovae: evidence for systematics? Astrophys. J. 623, 1011–1016 (2005)

    Article  ADS  Google Scholar 

  11. Khokhlov, A. M. Delayed detonation model for type Ia supernovae. Astron. Astrophys. 245, 114–128 (1991)

    ADS  CAS  Google Scholar 

  12. Iwamoto, K. et al. Nucleosynthesis in Chandrasekhar mass models for type Ia supernovae and constraints on progenitor systems and burning-front propagation. Astrophys. J. 125 (Suppl.). 439–462 (1999)

    Article  CAS  Google Scholar 

  13. Nomoto, K., Thielemann, F.-K. & Yokoi, K. Accreting white dwarf models of type I supernovae. III – carbon deflagration supernovae. Astrophys. J. 286, 644–658 (1984)

    Article  ADS  CAS  Google Scholar 

  14. Woosley, S. E. & Weaver, T. A. The physics of supernova explosions. Annu. Rev. Astron. Astrophys. 24, 205–253 (1986)

    Article  ADS  CAS  Google Scholar 

  15. Höflich, P. et al. Maximum brightness and postmaximum decline of light curves of type Ia supernovae: a comparison of theory and observations. Astrophys. J. 472, L81–L84 (1996)

    Article  ADS  Google Scholar 

  16. Mazzali, P. A., Röpke, F. K., Benetti, S. & Hillebrandt, W. A common explosion mechanism for type Ia supernovae. Science 315, 825–828 (2007)

    Article  ADS  CAS  Google Scholar 

  17. Benetti, S. et al. Supernova 2002bo: inadequacy of the single parameter description. Mon. Not. R. Astron. Soc. 348, 261–278 (2004)

    Article  ADS  Google Scholar 

  18. Branch, D., Fisher, A. & Nugent, P. On the relative frequencies of spectroscopically normal and peculiar type Ia supernovae. Astron. J. 106, 2383–2391 (1993)

    Article  ADS  CAS  Google Scholar 

  19. Maeda, K. et al. Nebular spectra and explosion asymmetry of type Ia supernovae. Astrophys. J. 708, 1703–1715 (2010)

    Article  ADS  CAS  Google Scholar 

  20. Fink, M. et al. Double-detonation sub-Chandrasekhar supernovae: can minimum helium shell masses detonate the core? Astron. Astrophys. (submitted); preprint at 〈〉 (2010)

  21. Stehle, M., Mazzali, P. A., Benetti, S. & Hillebrandt, W. Abundance stratification in type Ia supernovae – I. The case for SN 2002bo. Mon. Not. R. Astron. Soc. 360, 1231–1243 (2005)

    Article  ADS  CAS  Google Scholar 

  22. Wang, L., Baade, D. & Patat, F. Spectropolarimetric diagnostics of thermonuclear supernova explosions. Science 315, 212–214 (2007)

    Article  ADS  CAS  Google Scholar 

  23. Neill, J. D. et al. The local hosts of type Ia supernovae. Astrophys. J. 707, 1449–1465 (2009)

    Article  ADS  CAS  Google Scholar 

  24. Jha, S. et al. The type Ia supernova 1998bu in M96 and the Hubble constant. Astrophys. J. 125 (Suppl.). 73–97 (1999)

    Article  Google Scholar 

  25. Cappellaro, E. et al. Detection of a light echo from SN 1998bu. Astrophys. J. 549, L215–L218 (2001)

    Article  ADS  Google Scholar 

  26. Filippenko, A. V. et al. The subluminous, spectroscopically peculiar type Ia supernova 1991bg in the elliptical galaxy NGC 4374. Astron. J. 104, 1543–1556 (1992)

    Article  ADS  Google Scholar 

  27. Turatto, M. et al. The properties of the peculiar type Ia supernova 1991bg. I. Analysis and discussion of two years of observations. Mon. Not. R. Astron. Soc. 283, 1–17 (1996)

    Article  ADS  CAS  Google Scholar 

  28. Morrell, N., Folatelli, G. & Stritzinger, M. Supernova 2007on in NGC 1404. Cent. Bur. Electron. Telegr. 1131, (2007)

  29. Altavilla, G. et al. The early spectral evolution of SN 2004dt. Astron. Astrophys. 475, 585–595 (2007)

    Article  ADS  CAS  Google Scholar 

  30. Wang, X. et al. Improved distances to type Ia supernovae with two spectroscopic subclasses. Astrophys. J. 699, L139–L143 (2009)

    Article  ADS  CAS  Google Scholar 

Download references


We thank W. Hillebrandt for discussions. This study is partly based on observations obtained at the Gemini Observatory, Chile (GS-2009B-Q-8, GS-2008B-Q-32/40/46), the Magellan Telescopes, Chile, and by ESO Telescopes at the La Silla or Paranal Observatories under programme 080.A-0516. This research made use of the SUSPECT archive, at the Department of Physics and Astronomy, University of Oklahoma. This work was supported by World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan. K.M. was supported by a JSPS Grant-in-Aid for young scientists; S.B. acknowledges partial support from ASI contracts ‘COFIS’; M.S. was supported by the National Science Foundation; F.K.R. was supported through the Emmy Noether Program of the German Research Foundation and by the Cluster of Excellence ‘Origin and Structure of the Universe’; G.F. and M.H. acknowledge support from Iniciativa Cientifica Milenio and CONICYT programmes FONDECYT/FONDAP/BASAL; J.S. is a Royal Swedish Academy of Sciences Research Fellow supported by the Knut and Alice Wallenberg Foundation; and S.T. acknowledges support from the Transregional Collaborative Research Centre under the programme ‘The dark Universe’. The Dark Cosmology Centre is funded by the Danish National Research Foundation.

Author information

Authors and Affiliations



S.B. and K.M. found the relation between the velocity gradient and the nebular velocity, and initiated and organized the project. K.M. wrote the manuscript with the assistance of M.S., J.S., G.F. and S.T. S.B. is responsible for the late-phase spectrum of SN 1997bp. M.S., G.F. and M.H are responsible for acquisition and reduction of SN 2007on, SN 2007sr and SN 2009ab. F.K.R. and K.M. are responsible for the explosion simulation. All the authors contributed to discussions.

Corresponding author

Correspondence to K. Maeda.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Notes 1-3, Supplementary Table 1, Supplementary Figures 1-3 with legends and References. (PDF 365 kb)

PowerPoint slides

Rights and permissions

Reprints and permissions

About this article

Cite this article

Maeda, K., Benetti, S., Stritzinger, M. et al. An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae. Nature 466, 82–85 (2010).

Download citation

  • Received:

  • Accepted:

  • 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