A huge star has vanished without a trace, and without any supernova explosion, leaving astronomers puzzling over where it has gone.
One theory is that it collapsed to form a black hole, without an explosion.
“If true,” said team leader and PhD student Andrew Allan of Trinity College Dublin, “this would be the first direct detection of such a monster star ending its life in this manner.”
The other theory is that the star became less bright and partially obscured by dust, meaning it vanished from view.
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Astronomers had studied the mysterious massive star, located in the Kinman Dwarf galaxy, for 10 years between 2001 and 2011.
But when Trinity researchers used the ESO’s Very Large Telescope (VLT) to look at the galaxy again, they discovered it was gone.
“Instead, we were surprised to find out that the star had disappeared!” said Allan, who led a study of the star published in Monthly Notices of the Royal Astronomical Society.
Located 75 million light-years away in the constellation of Aquarius, the Kinman Dwarf galaxy is too far away for astronomers to see its individual stars, but they can detect the signatures of some of them.
From 2001 to 2011, the light from the galaxy consistently showed evidence that it hosted a “luminous blue variable” star 2.5 million times brighter than the Sun.
The traces were absent from the data the team collected in 2019, leaving them to wonder what had happened to the star.
“It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion,” said Allan.
“We may have detected one of the most massive stars of the local universe going gently into the night,” said team-member Jose Groh, also of Trinity College Dublin.
The old data indicated that the star in the Kinman Dwarf could have been undergoing a strong outburst period that likely ended sometime after 2011.
Based on their observations and models, the astronomers have suggested two explanations for the star’s disappearance and lack of a supernova, related to this possible outburst.
The outburst may have resulted in the luminous blue variable being transformed into a less luminous star, which could also be partly hidden by dust. Alternatively, the team said the star may have collapsed into a black hole, without producing a supernova explosion.
This would be a rare event – our current understanding of how massive stars die points to most of them ending their lives in a supernova.