When they reach a stage known as the luminous blue variable (LBV), the end as a supernova is usually imminent. The stars then hurl parts of their mass into space in a massive eruption, leaving a black hole. But when astronomers around Andrew Allan from Trinity College in Dublin wanted to observe such a star closer, they were amazed to find that the star, which was still visible in 2011 due to its luminosity of two and a half million suns, has disappeared.
At a distance of around 75 million light years, the star, which is native to the Kinman dwarf galaxy, cannot be observed directly. However, the spectrum of the galaxy reveals that it must contain a star of this type. At least that was the case between 2001 and 2011. As Allan and colleagues now write in the “Monthly Notices of the Royal Astronomical Society”, the characteristic trace is now missing in the spectrum of the galaxy.
What happened? The researchers are considering two possible explanations. For one thing, the star could be surrounded by a dense cloud of dust that shields its light so that its observation instrument at ESO’s Very Large Telescope on the Chilean Cerro Paranal could no longer catch it. On the other hand, the star could have collapsed directly into a black hole without a supernova – at least without an observable supernova. This would be a new phenomenon, especially since astronomers had previously assumed that the supernova of an LBV would be particularly violent. Instead, “we may have seen one of the most massive stars in the local universe gently breathe out his life,” said Allan’s colleague, Jose Groh, who also does research at Trinity College, in an ESO press release.
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