Using the very large telescope of the European Southern Observatory (VLT), astronomers discovered the absence of an unstable massive star in a dwarf galaxy. Scientists believe that this may indicate that the star has become less bright and partially obscured by dust. An alternative explanation is that a star fell into a black hole without the formation of a supernova. A study of this star was published today in the journal Monthly Notices of the Royal Astronomical Society.
Between 2001 and 2011, various groups of astronomers studied a mysterious massive star located in the dwarf Kinman galaxy. Their observations showed that the star is at a late stage of its development. Andrew Allan of Trinity College, Dublin, and his associates in Ireland, Chile and the United States wanted to learn more about how very massive stars end their lives. An object in Kinman’s dwarf galaxy seemed an ideal target. But when they sent the VLT ESO to a distant galaxy, they could no longer find the control coordinates of the star. Scientists were extremely surprised to learn that the star had disappeared.
Located at a distance of about 75 million light-years in the constellation Aquarius, Kinman’s dwarf galaxy is too far for astronomers to see its individual stars. However, scientists may discover the signatures of some of them. From 2001 to 2011, light from the galaxy constantly showed that it contained a star with a “luminous blue variable”, about 2.5 million times brighter than the sun. Stars of this type are unstable, from time to time showing sharp shifts in the spectrum and brightness. Even with these changes, the luminous blue variables leave certain traces that scientists can identify. But they were not in the data collected by the team in 2019, which made them think about what happened to the star.
The group simultaneously used four 8-meter VLT telescopes. But they could not find signs that previously indicated the presence of a luminous star. A few months later, the group tried the X-shooter tool, also on the VLT ESO, and again found no trace of the star.
“Perhaps we discovered one of the most massive stars in the local universe, gently leaving for the night. Our discovery would not have been possible without the use of the powerful 8-meter ESO telescopes, their unique instruments, and quick access to these opportunities after the recent agreement of Ireland to join the ESO”.
Jose Gro, Researcher at Trinity College Dublin
The research team then turned to older data collected using the X-shooter and the UVES tool on the VLT ESO, located in the Chilean Atacama Desert, and telescopes elsewhere. The ESO Scientific Archive allowed them to find and use data from the same facility obtained in different years.
Old data indicated that the star in the dwarf Kinman galaxy could survive a period of violent outbursts, which ended after 2011.
Based on their observations and models, astronomers have proposed two explanations for the disappearance of a star and the absence of a supernova. A flash could cause the luminous blue variable to turn into a less luminous star, which may also be partially obscured by dust. Alternatively, the team said the star could fall into a black hole without causing a supernova explosion. This would be a rare event: our current understanding of how massive stars die indicates that most of them end their supernova life.
Further research is needed to confirm what fate befell this star. Scheduled to begin work in 2025, the extremely large ESO (ELT) telescope will be able to observe stars in clusters of stars like the Keenman dwarf galaxy, helping to solve space puzzles.