Astronomers believe the star may have exploded and become less luminous – or turned into a black hole without going through the supernova stage.
Using the Very Large Telescope (VLT) of the European Southern Observatory (ESO), astronomers noted the disappearance of a massive, unstable blue star, located in the Kinman Dwarf Galaxy, in the constellation of Aquarius, 75 million light-years away from Earth.
Scientists believe this may indicate that the star has become less bright and has been partially covered by dust. Another hypothesis is that the star collapsed and turned into a black hole without producing a supernova. If the second hypothesis proves true, this would be the first direct detection of this type of event from a massive star.
Between 2001 and 2011, the mysterious star was studied by several scientists, and their observations indicated that, in addition to being 2.5 million times brighter than the Sun, it was in the final stage of its evolution. In 2019, when Andrew Allan of Trinity College Dublin, Ireland, and his collaborators decided to observe it to better understand how massive stars die, they couldn’t find it anymore.
In August 2019, the group turned the ESPRESSO instrument towards the star, using the VLT’s four eight-meter telescopes simultaneously. Even so, they were unable to find signs of the blue star in the Kinman Dwarf Galaxy. Months later, they used the X-shooter instrument to try to locate it, but again, they found no trace of the star. “It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion,” said Andrew Allan in a statement.
Data from previous studies have already indicated that the star could be experiencing a strong period of outbursts that probably ended some time after 2011. Luminous blue variable stars like this one tend to undergo violent outbursts throughout their life, causing spikes in the rate of mass loss and dramatic increases in luminosity. Therefore, scientists bet on both hypotheses.
The first – and most likely – is that, after exploding, the massive star has become a less luminous star, which may have been covered in dust as well. The other hypothesis is that the star may have turned into a black hole, skipping the supernova explosion stage. This would be a very rare event, since most massive stars are known to end their lives in a supernova.
Further research is needed to confirm what actually happened to the star. The inauguration of ESO’s Extremely Large Telescope (ELT), scheduled for 2025, could help scientists observe stars as far away as this one and solve this and other mysteries of the Cosmos.
The article on the discovery of the massive star’s disappearance will be published in the August issue of the Monthly Notices of the Royal Astronomical Society.