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

TL;DR

This paper proposes that the spectral diversity observed in Type Ia supernovae arises from viewing asymmetric explosions from different angles, implying that such asymmetry is a common feature and does not hinder their use as standard candles.

Contribution

It demonstrates that spectral evolution diversity in SNe Ia is due to asymmetric explosions viewed from various directions, supporting the idea of off-center ignition as a typical phenomenon.

Findings

Spectral diversity is caused by viewing angle of asymmetric explosions.

Asymmetry in explosions does not compromise SNe Ia as standard candles.

Ignition at an offset from the centre is likely a common feature in SNe Ia.

Abstract

Type Ia Supernovae (SNe Ia) form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates. This one-parameter behavior allows SNe Ia to be calibrated as cosmological `standard candles', and led to the discovery of an accelerating Universe. Recent investigations, however, have revealed that the true nature of SNe Ia is more complicated. Theoretically, it has been suggested that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf (WD) progenitor, possibly as a result of convection before the explosion. Observationally, the diversity seen in the spectral evolution of SNe Ia beyond the luminosity decline-rate relation is an unresolved issue. 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 in using SNe Ia as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre of is a generic feature of SNe Ia.