Star appears to have vanished in a failed supernova

A massive star in a nearby galaxy that reached the end of its life appears to have vanished rather than blown up, forming a black hole in what astronomers think is a rare way.

The most common black holes in our galaxy begin as stars. When these stars explode in a supernova, they can leave behind a black hole. But it is thought that black holes can also form from stars that fail to go supernova, instead simply collapsing under their own mass and producing a black hole directly.

In 2024, Kishalay De at Columbia University in New York and his colleagues observed an unusually bright star called M31-2014-DS1 in the nearby galaxy Andromeda that was around 20 times as massive as our sun. The star appeared to grow briefly brighter in 2014, before becoming dramatically dimmer between 2017 and 2020. De and his colleagues thought this pattern of brightening and then fading matched predictions for a failed supernova producing a black hole, but there was no sign of the black hole itself, such as tell-tale X-ray radiation.

Now, De and his team have observed M31-2014-DS1 with the James Webb Space Telescope (JWST) and the Chandra X-ray Observatory, finding a faint, red object where the star once was that is only around 8 per cent as bright as the original star and is shrouded in a cocoon of dust moving rapidly outwards. This fits with what astronomers think a failed supernova making a black hole would look like. De and his team declined to comment for this story because their research hasn’t been peer-reviewed yet.

In a separate study analysing the same JWST data, Emma Beasor at Liverpool John Moores University, UK, and her colleagues found that the case for M31-2014-DS1 undergoing a failed supernova that produced a black hole was murkier, and that the observations could just as easily be the result of two stars merging, which would also produce a small outburst followed by a dimming and lots of dust.

“The predictions for what a failed supernova looks like overlap quite significantly with what we might expect from two stars colliding and producing loads of dust,” says Beasor.

However, both scenarios would still be exotic phenomena, she says. “We don’t see stars that fade this significantly very often.”

“In either explanation, this is exciting. The visible star really has gone away,” says Gerard Gilmore at the University of Cambridge. “For many years, searches for disappearing massive stars led to ambiguous results. Now, the full power of multi-wavelength time-domain astronomy is on show and making progress.”

The only surefire way to say whether a black hole has been formed is to identify X-ray radiation, says Gilmore, which can’t currently be seen at the location of M31-2014-DS1. However, being able to study the aftermath of a dimmed star with a powerful telescope like JWST will allow us to find out what happened, he says. “We are on the verge of discovering at least one of the final fates of massive stars, an amusingly Cheshire cat way to go.”

References: arXiv, DOI: 10.48550/arXiv.2601.0577 and DOI: 10.48550/arXiv.2601.05317

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