One of the most massive stars in local universe may have disappeared
A star that shone with 2.5 million times the light of our Sun has disappeared from the night sky. It is possible that the star collapsed into a black hole without first triggering a supernova – a rare event, even in the context of dying stars.
The errant star is, or was, located in the Kinman Dwarf galaxy in the constellation of Aquarius, some 75 million light-years from Earth. At such vast distances, it isn’t possible to clearly see individual stars. However truly massive stars – such as the one at the center of the new study – shine so brightly that they leave evidence of their presence in the form of a light signature, that tells astronomers that they're there.
In the future, astronomers will be able to make more detailed studies of individual stellar bodies hiding in distant dwarf galaxies like Kinman using the ESO’s upcoming Extremely Large Telescope, which is slated for completion in the year 2025.
Luminous blue variable stars are enormous by the standards of our Sun, and shine incredibly brightly. However, magnificent as they are, they are also unstable, and prone to dramatic outbursts during which they lose mass at a highly accelerated rate.
From 2001-2011 the star was observed by astronomers looking to heighten our understanding of the life cycles of monster stars and their eventual fates. In 2019, a team of international scientists sought to continue this work by turning the powerful gaze of the ESO’s Very Large Telescope (VLT) on the variable star. To their surprise, the light signature of the star had disappeared.
The seemingly sudden disappearance of the star was unusual, as, according to the researchers, such a massive stellar body would be expected to explode in a cataclysmic supernova upon ending its life cycle.
“We may have detected one of the most massive stars of the local Universe going gently into the night,” comments team-member Jose Groh of Trinity College Dublin, who was one of the authors of the new paper.
With their own observations turning up no evidence of the star, the researchers turned to older data that was captured in 2002 and 2009 by two powerful spectrometers mounted on the four telescopes that make up the VLT.
The archived data suggested that the star may have been experiencing a powerful outburst that caused the star to lose a huge amount of mass, and ended sometime after 2011.
Based on their analysis, the team put forward two potential reasons for the stellar disappearing act, and the absence of a visible supernova.
At the close of the outburst event, the luminous blue variable star could have transitioned into a less luminous stellar body that was cloaked in a thick view of dust comprising previously cast off matter.
The second explanation put forth by the team is more dramatic – the star could have ended its stellar life by quietly collapsing into an enormous black hole. If the latter is true, it would be the first time that such a massive, extremely bright star would have ever been detected ending its life in this way.
However, the researchers can’t rule out the possibility that the star went supernova in the period between 1995 and 1998 when no observations were available. In that case the signature of the star that astronomers thought they were seeing between 2001-2011 would have been from an interaction between the supernova ejecta and the dense circumstellar medium.
Further observations will be needed to determine the fate of the mysterious luminous blue variable star that once brightened the Kinman Dwarf. The phantom star will be an attractive target for astronomers making use of the Extremely Large Telescope when it goes into service.
The paper has been published in the Monthly Notices of the Royal Astronomical Society.
The video below zooms in on the Kinman Dwarf galaxy from the perspective of Earth.