A Star Vanishes: Possible Evidence of a 'Failed Supernova'?

Some massive stars may go out with a fizzle, not a bang.

A star that winked out of view could be a “failed supernova,” a stellar explosion that petered out instead of fully detonating, a new study reports. If real, the failed supernova would mark the birth of a black hole.

At the ends of their lives, massive stars explode in dazzling outbursts known as supernovas, kicked off when the star’s core collapses. But sometimes, scientists suspect, there’s not enough oomph for a full explosion, resulting in a star that switches off without fireworks. 

No one has ever conclusively detected a failed supernova. But now, there’s a new candidate. Visible light from the star, a supergiant spotted in the neighboring Andromeda galaxy, faded dramatically beginning in 2016, fully vanishing by 2023, MIT astrophysicist Kishalay De and colleagues report in a paper submitted October 18 to arXiv.org. 

“It’s what you expect [from a failed supernova]. You have something there that’s bright and luminous and looks like a massive star, and then it disappears,” says astrophysicist Morgan Fraser, who was not involved with the research. 

But the discovery isn’t yet conclusive. “There’s a lot of other things … that can look a little bit similar and mislead you,” says Fraser, of University College Dublin. For example, clouds of dust can shroud stars, dimming them (SN: 6/16/21). 

Another puzzle: Scientists expect to see some tumult from a failed supernova, as the star’s outer layers should puff off. But De and colleagues saw no visible light show. To explain that, the researchers suggest the star had previously been stripped of some of its outer envelope of hydrogen. De declined to comment as the study has not yet been peer reviewed.

In a failed supernova, a star dies without producing an explosion (illustrated). After the star’s core collapses into a black hole, material left over from the star falls into the black hole (center) producing a glow of infrared light.

Conclusively catching a supernova fail would be an astronomical win. “For the moment, it’s the only feasible way of actually seeing a black hole being formed,” says astrophysicist Christopher Kochanek of the Ohio State University. 

Kochanek and colleagues previously reported a possible failed supernova (SN: 9/20/16). But scientists are still working to rule out other possible explanations for it. Follow-up observations with the James Webb Space Telescope, or JWST, showed an infrared glow, Kochanek and colleagues reported in the Feb. 20 Astrophysical Journal. That infrared light could be emitted by residual matter falling into a newly formed black hole. Or it could be due to something more commonplace than a failed supernova, such as two stars merging and kicking up a cloud of dust. 

Likewise, some infrared glow persisted from the newfound vanished star, even though the visible light disappeared. That leaves it in a similar limbo about whether it’s a failed supernova or not. “With the sparse observations that we have … it’s very difficult to tell the difference,” says astrophysicist Griffin Hosseinzadeh of the University of California, San Diego, who was not involved with the research.

Additional data from JWST could help nail down the origins of both purported failed supernovas. Scientists could also look for X-rays, which could be produced if there’s a black hole swallowing matter.

Understanding stars’ death throes is important for determining how galaxies get their populations of black holes and neutron stars — ultradense remnants left behind by successful supernovas (SN: 2/22/24). And stellar demise is also important for how the chemical elements formed in stars get blasted throughout the cosmos. 

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Eventually, scientists hope to be able to predict the ultimate fate of a star. “What we’d like to know is, as a function of the mass of the star when it’s born, is it going to be a supernova and make a neutron star, or is it going to be a failure and make a black hole?” says astrophysicist Stanford Woosley of the University of California, Santa Cruz, who was not involved with the research. “The whole idea of black hole birth, and what it looks like and what different masses of stars produce, those are critical issues.”