Evidence of the role of helium in triggering type Ia supernovae

The supernova MUSSES1604D (Image courtesy Institute of Astronomy, the University of Tokyo)
The supernova MUSSES1604D (Image courtesy Institute of Astronomy, the University of Tokyo)

An article published in the journal “Nature” describes a research that provides evidence that the explosion of a supernova was triggered by the detonation of a helium layer on the surface of a white dwarf. A team of researchers led by Ji-an Jiang of the University of Tokyo used the Subaru telescope with follow-up observations using the Gemini-North telescope to study MUSSES1604D, a type Ia supernova. Their conclusion is that a white dwarf stole helium from a companion star and it formed a layer that at one point exploded, triggering the supernova.

Scientists have been debating for decades about the mechanisms that trigger type Ia supernovae. The hypotheses are the accumulation of materials around a white dwarf coming from a companion star or the violent merger between two white dwarfs. Research in the last few years conducted thanks to the the last generations instruments led to evidence of supernova cases triggered by both mechanisms. However, there are still points to be clarified and this new research can bring some progress.

The researchers have been specifically looking for recent type Ia supernovae using the Subaru Telescope’s Hyper Suprime-Cam camera, which captures a large area of ​​the sky. In this way they discovered 100 possible supernovae in one night and among them they identified a type Ia case exploded only within a day before their observation.

That supernova proved to be more intriguing than expected because it showed a brilliant flash on the first day that according to the researchers is related to the nature of the explosion. The picture shows observations of the supernova MUSSES1604D from April 2016 with the Subaru telescope and a month later with the Gemini-North telescope with its light curves. The green circles indicate the supernova stage during the observations.

The researchers verified that the data obtained from the observations matched to the effect on the brightness of the supernova that was called MUSSES1604D by a helium explosion on its surface calculated using a supercomputer. This is an important result because for the first time it was possible to find some evidence in favor of a theory on the mechanism at work for at least one type of supernova.

This research is an important step in understanding at least a part of type Ia supernovae but is far from over. For example, the nature of the companion of the white dwarf that became a supernova is still to be established. Above all, further tests on the theory of the role of helium are needed, so further observations on other supernovae will follow.

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