Short-lived light sources discovered in the sky
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An international team of researchers have used publicly available data with images of the sky dating as far back as the 1950s to detect and analyse objects that have disappeared over time. They have particularly looked for objects that may have existed in old military sky catalogues from the 1950s but are not to be found again in modern sky surveys. Among the physical indicators they were looking for were stars that have vanished in the Milky Way
"Finding a star that really vanishes – or a star that appears out of nowhere! – would be an outstanding discovery and would certainly imply new astrophysics beyond our current knowledge," says project leader Beatriz Villarroel, Stockholm University and Instituto de Astrofísica de Canarias, Spain.
“Various co-authors from Uppsala University have been working on the information technology challenges related to this study. IT master’s student Johan Soodla, who is second author, has contributed significantly to the result. Earlier research meetings were supported by the Department of Information Technology and its machine learning arena,” says Kristiaan Pelckmans, researcher at the Department of Information Technology, Uppsala University.
When a star dies it either undergoes very slow changes and becomes a white dwarf or it dies with a sudden bright explosion, i.e. it becomes a supernova. A vanishing star would be an ‘impossible phenomenon’ that could be attributed either to new astrophysical phenomena or to extraterrestrial activity. Indeed, the only non-ETI (extraterrestrial intelligence) explanation for a vanishing star would be an exceedingly rare event called a ‘failed supernova’. A failed supernova is theoretically predicted to occur when a very massive star collapses into a black hole without any visible explosion. Other physical indicators of ETI activity that the authors are looking for are signs of red interstellar communication lasers and Dyson spheres. A Dyson sphere is a hypothetical giant structure surrounding a star to harness its energy.
"As a by-product, this project has the potential to discover rare, extremely variable objects. These could shed light on rapid hard-to-observe phases of stellar evolution and active galactic nuclei,” says co-author Sébastien Comerón, Oulu University, Finland.
The researchers have carefully examined about 15 per cent of the 150,000 candidate objects in the available data and found approximately 100 red transients – very variable objects or events in the sky. Some of these objects appear to have flared up at least 8–9 magnitudes, becoming several thousand times brighter, in a very short time.
"We are very excited about following up on the 100 red transients we have found," says Beatriz Villarroel.
"But we are clear that none of these events have shown any direct signs of being due to ETI. We believe that they are natural, if somewhat extreme, astrophysical sources," says Martin López Corredoira, co-author of the paper, Instituto de Astrofísica de Canarias, Spain.
The researchers are now looking at the possibility of arranging a citizen science project, aided by artificial intelligence. To be able to examine all the 150,000 candidates that have been identified from the material, they must speed up the process of identifying anomalies in the images.
"We hope to get help from the community to look through the images as part of a citizen science project. We are looking at ways to do that right now and that will be something we will be able to talk more about at a later date," says Lars Mattsson, Stockholm University.
Linda Koffmar