Impending explosion: Massive stars warn when they’re about to go supernova

In this new study, the researchers determined that massive stars (typically between 8 and 20 solar masses) in the “red supergiant” phase will suddenly become about a hundred times fainter in visible light a few months before they die. This dimming is caused by a sudden accretion of material around the star, obscuring its light

An artist’s impression of the Beetlejuice Supernova. Credit: European Southern Observatory/L. Calçada

Astronomers from Liverpool John Moores University and the University of Montpellier have developed an “early warning” system that will warn when a massive star is about to end its life in a supernova explosion. The work was published on October 13, 2022 in the journal Monthly Notices of the Royal Astronomical Society.

In this new study, the researchers determined that massive stars (typically between 8 and 20 solar masses) in the final stage of their lives, the so-called “red supergiant” stage, will suddenly become about a hundred times fainter in visible light a few months before they die. This dimming is caused by a sudden accretion of material around the star, obscuring its light.

Red supergiants are stars of spectral type K or M with a supergiant luminosity classification (Yerkes classification I). In terms of volume, they are the largest stars in the universe. But they are not the biggest in terms of mass or luminosity. Beetlejuice and Antares are the brightest and best known red supergiants.

The star turns into a cocoon

Until now, they didn’t know how long it takes for a star to accumulate this material. For the first time, scientists have now simulated what red supergiants might look like embedded in these pre-explosion “bulbs”.

Old telescope archives show that there are images of stars that exploded around a year after the image was taken. The stars look normal in these images, meaning they could not yet have accreted the theoretical cocoon around them. It follows that the tuber is collected in less than a year, which is considered very fast.

Benjamin Davies of John Moores University in Liverpool, lead author of the paper, says: “The dense material dims the star almost completely, making it a hundred times fainter in the visible part of the spectrum. This means that the day before the star explodes, it will probably be impossible to see which is there”. He adds: “Until now, we could get detailed observations of supernovae only hours after they had already occurred. With this early warning system we can prepare to watch them in real time, point the world’s best telescopes at the precursor stars and watch them tear apart, literally, before our eyes”.