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The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star


The accelerating expansion of the Universe, and the need for dark energy, were inferred from observations1,2 of type Ia supernovae. There is a consensus that type Ia supernovae are thermonuclear explosions that destroy carbon–oxygen white dwarf stars that have accreted matter from a companion star3, although the nature of this companion remains uncertain. These supernovae are thought to be reliable distance indicators because they have a standard amount of fuel and a uniform trigger: they are predicted to explode when the mass of the white dwarf nears the Chandrasekhar mass4 of 1.4 solar masses (M). Here we show that the high-redshift supernova SNLS-03D3bb has an exceptionally high luminosity and low kinetic energy that both imply a super-Chandrasekhar-mass progenitor. Super-Chandrasekhar-mass supernovae should occur preferentially in a young stellar population, so this may provide an explanation for the observed trend that overluminous type Ia supernovae occur only in ‘young’ environments5,6. As this supernova does not obey the relations that allow type Ia supernovae to be calibrated as standard candles, and as no counterparts have been found at low redshift, future cosmology studies will have to consider possible contamination from such events.

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Figure 1: The lightcurve of SNLS-03D3bb.
Figure 3: Keck LRIS spectrum of SNLS-03D3bb at two days after maximum light compared to a spectrum of the normal type Ia supernova SN 1994D.
Figure 2: Bolometric luminosity versus implied 56Ni mass for SNLS-03D3bb and low-redshift type Ia supernovae7.
Figure 4: Inferred Ni mass versus Si ii 615 nm velocity.

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SNLS relies on observations with MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada–France–Hawaii Telescope (CFHT). We used data products from the Canadian Astronomy Data Centre as part of the CFHT Legacy Survey. Some data were obtained at the W. M. Keck Observatory. We acknowledge support from NSERC, NERSC, CIAR, CNRS/IN2P3, CNRS/INSU, CEA and the DOE.

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Correspondence to D. Andrew Howell.

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Andrew Howell, D., Sullivan, M., Nugent, P. et al. The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star. Nature 443, 308–311 (2006).

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