The birth of a new supernova, captured serendipitously by an amateur astronomer who was testing a new camera, is reported in Nature this week. This chance observation provides an opportunity to learn more about the properties of the star that exploded and offers new insights into supernova evolution.

The surge of light at the birth of a new supernova can provide information about the final evolution and structure of the exploding star. However, it is hard to predict when supernovae are about to explode, which hinders the detection of this brief ‘shock breakout’ phase. Most supernovae are observed at an undetermined time after the explosion.

On 20 September 2016, amateur astronomer Victor Buso was testing a new camera mounted to a telescope pointing towards a spiral galaxy called NGC 613 while a supernova was being born. Less than one day later, Melina Bersten and colleagues performed extensive monitoring of the supernova and studied its evolution. The brightness of light emitted by the exploding star increased very rapidly, a signal that the authors suggest corresponds to the long-sought shock-breakout phase.

They classify the explosion as a type IIb supernova and their analysis suggests that the progenitor star was slightly more massive than another well-studied type IIb supernova, known as SN 2011dh. Moreover, modelling based on the discovery data allows the authors to distinguish between distinct supernova evolution phases that are regulated by different physical processes. The authors conclude that further analyses of the shock-breakout signal could potentially provide more information on the progenitor structure and the physical processes that occur during the emergence of the shock.