Astronomers using the Very Large Telescope (VLT) have found that an unstable massive star has disappeared from a nearby dwarf galaxy. The only question is whether she hid behind a thick cloud of dust or fell into a black hole without exploding as a supernova.
If this was the case, it would be the first time that the end of the star’s life was observed, ‘says Andrew Allan, lead author of the discovery and PhD student at Trinity College in Dublin.
In 2001-2011, many different research teams studied the mysterious massive star found in the Kinman dwarf galaxy. All studies indicated that the star is in a late stage of evolution. Allan and his colleagues planned to study how such massive stars end their lives. The object in a nearby galaxy seemed to be the perfect target for observation. However, when the VLT telescope’s eyes were turned to the galaxy in 2019, it turned out that there was no trace of the star.
To our surprise, it turned out that the star has disappeared – adds Allan.
Kinman’s dwarf galaxy 75 million light-years away from Earth toward the constellation of Aquarius. It’s far too far to see individual stars. Despite this, scientists are able to detect the signatures of some. In the years 2001-2011, radiation from the galaxy constantly showed evidence of the presence of a bright blue variable star 2.5 million times brighter than the Sun. Stars of this type are extremely unstable, and sometimes are characterized by rapid changes in brightness. However, even with these changes, these stars leave characteristic traces that can be easily detected from Earth. In 2019, they were no longer noticed.
The disappearance of such a massive star without a supernova explosion is very unusual – informs Allan.
In August 2019, researchers turned the galaxy to four 8-meter mirrors of the VLT telescope with the ESPRESSO instrument installed. In the collected data, however, nothing indicated the presence of bright blue stars. A few months later, researchers tried again, this time using a newer X-shooter instrument.
Nothing of that. The star has disappeared
It is quite possible that we have just observed the disappearance of one of the most massive stars in the local Universe. We would not be able to observe it were it not for the powerful VLT mirrors and access to them, which we obtained immediately after joining Ireland to the European Southern Observatory
– says Jose Groh, also from Trinity College.
Astronomers have decided to analyze older data collected using X-shooter and UVES instruments installed on board the VLT in the Chilean Atacama Desert. The star was clearly visible in the archived data from 2002 and 2009. However, there was no trace of it in the 2019 data.
Earlier data indicate that the star in the Kinman dwarf galaxy was going through a period of strong flares, which most likely ended after 2011. Bright blue variable stars of this type often experience gigantic flares in which the rate of mass loss and brightness increases rapidly.
The star either hid or turned into a black hole
Based on observations and models, astronomers have proposed two explanations for the disappearance of the star and the absence of a supernova. One of the flares could make the bright blue variable star much darker or partially obscured by dust. The second hypothesis is that the star could collapse under its own gravity into a black hole without causing a supernova. This would be an extremely rare event: it is now assumed that massive stars usually end their lives in a supernova explosion.
Additional research will be needed to clarify the final fate of the star. The Extremely Large Telescope (ELT), which will begin observing in 2025, will be able to separate individual stars in distant galaxies such as the Kinman Dwarf Galaxy – maybe then this puzzle can be solved.
She was a star – there is no star. It is not known where she went