A star vanished in Andromeda galaxy. Now a strange red source is puzzling astronomers

A yellow supergiant star, M31-2014-DS1, vanished from the Andromeda Galaxy between 2014 and 2018, and astronomers don't have an answer about what happened to it. Two teams of researchers studied the event and recently came up with possible explanations for its disappearance, IFL Science reported. One of the teams used the James Webb Space Telescope to understand what could have happened to the star that was observed shining brightly in 2014. They state in their preprint, which has yet to be peer reviewed, that it likely turned into a black hole without undergoing a supernova, the explosive death of a star. These bright bodies in the cosmos have a way to end their lives. Once their fuel runs out, they burst into a supernova, putting on an extremely bright show. However, nothing of the sort was seen with M31-2014-DS1. The researchers think that it was a failed supernova.

Explaining the two scenarios, they wrote that "stellar-mass black holes (BHs) are understood to represent the end states of massive stellar evolution". Theoretically speaking, there are "multiple pathways to their formation. These include both successful terminal explosions – in which the progenitor star ejects most of its core and outer envelope in a core-collapse supernova – and failed explosions, where the star undergoes near-complete implosion with little accompanying mass ejection."

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Red light in place of missing star

The team used JWST and the Chandra X-ray Observatory to see what was left and found an "extremely red source" in place of the star. Its brightness is only around 7–8 per cent of the original star. There is also a shell of dust surrounding the red source that stretches out to a whopping 40-200 times the distance between Earth and Sun. The team thinks the red spot is material ejected by the star that is now falling back into a newly formed black hole. However, the accretion is not seen in X-ray observations, making the failed supernova theory questionable.

Another team made observations that challenge the failed supernova theory.

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Why it could not be a failed supernova

"Several observational details challenge the interpretation of M31-2014-DS1 as a failed SN," the team wrote in their paper. They say that if it went directly from being a star to a black hole without a supernova, then the luminosity from fallback accretion should decline as the accretion rate decreases. But not much of a fall has been noticed in the brightness of the source. They used the Chandra telescope to find the X-rays, but none were detected. Both studies have been posted on the pre-print server arXiv.

Scientists say the dust could be hampering a proper view of the zone. Which brings them to a second explanation - a stellar merger. The team says it is possible that two stars collided and created this dust which is making it hard to see what is going on there. They believe once the dust settles, the main source might become visible.