Scientists discover a supernova takes place inside a cloud of circumstellar matter

University of Chile researchs shifts our understanding of the last stages of stellar evolution

Understanding of the last stage of stellar evolution has been turned on its head thanks to fresh research from an international team of scientists.

The researchers compared observation results to simulation models and found that, in many cases, the explosion of a red supergiant star - called a "supernova" - actually takes place inside a thick cloud of circumstellar matter, also known as circumstellar disks.

This, they note, is a completely fresh discovery.

The global astronomy team was led by the University of Chile's Francisco Förster. They used the University's famous Blanco Telescope and found 26 supernovae coming from red supergiants.

Their goal was to study the shock breakout, that is, a brief flash of light preceding the main supernova explosion. But they could not find any signs of this phenomenon. On the other hand, 24 of the supernovae brightened faster than expected.

To find out why this was happening, researcher Takashi Moriya from the National Astronomical Observatory of Japan (NAOJ) simulated 518 models of supernovae brightness variations and compared them with the observational results.

His team found that models with a layer of circum-stellar matter about ten per cent the mass of the Sun surrounding the supernovae matched the observations well, and it was this circumstellar matter which hides the shock breakout, trapping its light.

The subsequent collision between the supernova ejecta and the circumstellar matter creates a strong shock wave that produces extra light, causing it to brighten more quickly.

"Near the end of its life, some mechanism in the star's interior must cause it to shed mass that then forms a layer around the star," explained Moriya.

"We don't yet have a clear idea of the mechanism causing this mass loss. Further study is needed to get a better understanding of the mass loss mechanism.

"This will also be important in revealing the supernova explosion mechanism and the origin of the diversity in supernovae."

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