An asymmetric explosion as the origin of spectral evolution diversity in type Ia supernovae.
Maeda, K. 1; Benetti, S. 2; Stritzinger, M. 3,4; Ropke, F. K. 5; Folatelli, G. 6; Sollerman, J. 4,7; Taubenberger, S. 5; Nomoto, K. 1; Leloudas, G. 4; Hamuy, M. 6; Tanaka, M. 1; Mazzali, P. A. 5,8; Elias-Rosa, N. 9
[Letter] Nature. 466(7302):82-85, June 30, 2010.

(Format: HTML, PDF)

: Type Ia supernovae form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates 1. This one-parameter behaviour allows type Ia supernovae to be calibrated as cosmological 'standard candles', and led to the discovery of an accelerating Universe 2 3. Recent investigations, however, have revealed that the true nature of type Ia supernovae is more complicated. Theoretically, it has been suggested 4 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 explosion 4. Observationally, the diversity seen in the spectral evolution of type Ia supernovae beyond the luminosity-decline-rate relation is an unresolved issue 9 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.

(C) 2010 Nature Publishing Group