An important and perhaps critical clue to the mechanism driving the explosion of massive stars as supernovae is provided by the accumulating evidence for asymmetry in the explosion. Indirect evidence comes from high pulsar velocities1, associations of supernovae with long-soft γ-ray bursts2,3, and asymmetries in late-time emission-line profiles4. Spectropolarimetry provides a direct probe of young supernova geometry, with higher polarization generally indicating a greater departure from spherical symmetry5,6. Large polarizations have been measured for ‘stripped-envelope’ (that is, type Ic; ref. 7) supernovae, which confirms their non-spherical morphology8,9; but the explosions of massive stars with intact hydrogen envelopes7,10 (type II-P supernovae) have shown only weak polarizations at the early times observed11,12. Here we report multi-epoch spectropolarimetry of a classic type II-P supernova that reveals the abrupt appearance of significant polarization when the inner core is first exposed in the thinning ejecta (∼90 days after explosion). We infer a departure from spherical symmetry of at least 30 per cent for the inner ejecta. Combined with earlier results, this suggests that a strongly non-spherical explosion may be a generic feature of core-collapse supernovae of all types, where the asphericity in type II-P supernovae is cloaked at early times by the massive, opaque, hydrogen envelope.
This is a preview of subscription content, access via your institution
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Chatterjee, S. et al. Getting its kicks: A VLBA parallax for the hyperfast pulsar B1508 + 55. Astrophys. J. 630, L61–L64 (2005)
Galama, T. J. et al. An unusual supernova in the error box of the gamma-ray burst of 25 April 1998. Nature 395, 670–672 (1998)
Matheson, T. et al. Photometry and spectroscopy of GRB 030329 and its associated supernova 2003dh: The first two months. Astrophys. J. 599, 394–407 (2003)
Mazzali, P. A. et al. An asymmetric, energetic type Ic supernova viewed off-axis and a link to gamma-ray bursts. Science 308, 1284–1287 (2005)
Shapiro, P. R. & Sutherland, P. G. The polarization of supernova light—A measure of deviation from spherical symmetry. Astrophys. J. 263, 902–924 (1982)
Höflich, P. Asphericity effects in scattering dominated photospheres. Astron. Astrophys. 246, 481–489 (1991)
Filippenko, A. V. Optical spectra of supernovae. Annu. Rev. Astron. Astrophys. 35, 309–355 (1997)
Leonard, D. C. & Filippenko, A. V. in Supernovae as Cosmological Lighthouses (eds Turatto, M., Benetti, S., Zampieri, L. & Shea, W.) 330–336 (ASP, San Francisco, 2005)
Wang, L., Baade, D., Höflich, P. A. & Wheeler, J. C. Spectropolarimetry of the Type Ic supernova SN 2002ap in M74: More evidence for asymmetric core collapse. Astrophys. J. 592, 457–466 (2003)
Leonard, D. C. et al. The distance to SN 1999em in NGC 1637 from the expanding photosphere method. Publ. Astron. Soc. Pacif. 114, 35–64 (2002)
Leonard, D. C., Filippenko, A. V., Ardila, D. R. & Brotherton, M. S. Is it round? Spectropolarimetry of the Type II-P supernova 1999em. Astrophys. J. 553, 861–885 (2001)
Leonard, D. C. & Filippenko, A. V. Spectropolarimetry of the Type II supernovae 1997ds, 1998A, and 1999gi. Publ. Astron. Soc. Pacif. 113, 920–936 (2001)
Nakano, S., Itagaki, K., Bouma, R. J., Lehky, M. & Hornoch, K. Supernova 2004dj in NGC 2403. IAU Circ. 8377 (2004)
Patat, F., Benetti, S., Pastorello, A., Filippenko, A. V. & Aceituno, J. Supernova 2004dj in NGC 2403. IAU Circ. 8378 (2004)
Freedman, W. L. et al. Final results from the Hubble Space Telescope key project to measure the Hubble constant. Astrophys. J. 553, 47–72 (2001)
Eastman, R. G., Woosley, S. E., Weaver, T. A. & Pinto, P. A. Theoretical light curve of a Type II-P supernova. Astrophys. J. 430, 300–310 (1994)
Höflich, P., Wheeler, J. C., Hines, D. C. & Trammell, S. R. Analysis of the polarization and flux spectra of SN 1993. J. Astrophys. J. 459, 307–321 (1996)
Jeffery, D. J. Analysis of SN 1987A polarimetry. Astrophys. J. 375, 264–287 (1991)
Leonard, D. C., Li, W., Filippenko, A. V., Foley, R. J. & Chornock, R. Evidence for spectropolarimetric diversity in Type Ia supernovae. Astrophys. J. 632, 450–475 (2005)
Wheeler, J. C., Meier, D. L. & Wilson, J. R. Asymmetric supernovae from magnetocentrifugal jets. Astrophys. J. 568, 807–819 (2002)
Maeda, K. et al. Explosive nucleosynthesis in aspherical hypernova explosions and late-time spectra of SN 1998bw. Astrophys. J. 565, 405–412 (2002)
Höflich, P. A., Baade, D., Khokhlov, A. M., Wang, L. & Wheeler, J. C. in A Massive Star Odyssey: from Main Sequence to Supernova (eds van der Hucht, K. A., Herrero, A. & Esteban, C.) Proc. IAU Symp. 212 387–394 (ASP, San Francisco, 2003)
Elmhamdi, A. et al. Photometry and spectroscopy of the Type IIP SN 1999em from outburst to dust formation. Mon. Not. R. Astron. Soc. 338, 939–956 (2003)
Chugai, N. N. et al. Optical observations of the Type IIP supernova 2004dj: Evidence for the asymmetry of 56Ni ejecta. Astron. Lett. 31, 792–805 (2005)
Höflich, P. A., Khokhlov, A. & Wang, L. in 20th Texas Symp. on Relativistic Astrophysics (eds Wheeler, J. C. & Martel, H.) 459–471 (AIP, New York, 2001)
Höflich, P. A. Remarks on the polarization observed in SN 1993J. Astrophys. J. 440, 821–829 (1995)
Wang, X. et al. The progenitor of SN 2004dj in a star cluster. Astrophys. J. 626, L89–L92 (2005)
Li, W., Van Dyk, S. D., Filippenko, A. V. & Cuillandre, J.-C. On the progenitor of the Type II SN 2004et in NGC 6946. Publ. Astron. Soc. Pacif. 117, 121–131 (2005)
Heger, A., Fryer, C. C., Woosley, S. E., Langer, N. & Hartmann, D. H. How massive stars end their life. Astrophys. J. 591, 288–300 (2003)
Maeder, A. & Conti, P. S. Massive star populations in nearby galaxies. Annu. Rev. Astron. Astrophys. 32, 227–275 (1994)
We thank D. Kasen for discussions. Support for this research was provided by the National Science Foundation, NASA, and the Sylvia and Jim Katzman Foundation. A.V.F. is grateful for a Miller Research Professorship at UC Berkeley, during which part of this work was completed.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
About this article
Cite this article
Leonard, D., Filippenko, A., Ganeshalingam, M. et al. A non-spherical core in the explosion of supernova SN 2004dj. Nature 440, 505–507 (2006). https://doi.org/10.1038/nature04558
This article is cited by
Space Science Reviews (2018)