Scientists are investigating strange blinking lights in the sky for indications that they are signs of "interstellar communication lasers" or alien structures.
A number of appearing and vanishing objects have been spotted among the stars and are puzzling the scientists who are trying to understand what they are.
Astronomers believe the lights will probably be coming from "natural, if somewhat extreme, astrophysical sources". But they are yet to find any explanation, after discovering 100 of the lights.
Whatever scientists find it likely to change our understanding of space, potentially ushering in a "new astrophysics", scientists said.
"The implications of finding such objects extend from traditional astrophysics fields to the more exotic searches for evidence of technologically advanced civilisations," the authors write in the new paper.
In the research, detailed in a new paper published in the Astrophysical Journal, scientists looked at publicly available images of the sky dating as far back as the 1950s, such as old military sky catalogues. They compared those historical observations with modern sky surveys, looking for physical indicators that included stars that appear to have disappeared from the Milky Way.
"Finding an actually vanishing star – or a star that appears out of nowhere! – would be a precious discovery and certainly would include new astrophysics beyond the one we know of today", said project leader Beatriz Villarroel, Stockholm University and Instituto de Astrofísica de Canarias, Spain.
Usually, a dying star will change very slowly to become a white dwarf, or die with a sudden explosion as a supernova. A vanishing star would therefore indicate something else entirely: either a new, natural astrophysical phenomena or extraterrestrial activity elsewhere in the universe.
The only known natural explanation for such a vanishing star would be a "failed supernova", which has been theoretically predicted to be what happens when a very massive star collapses into a black hole, without sending out any kind of explosion. But those are very rare.
Possible extraterrestrial explanations include lasers being sent through the universe as part of communication between stars, or Dyson spheres, which are theoretical structures that alien civilisations could build around a star and harness its energy. While both are hypothetically possible, no evidence for either has ever been discovered.
Scientists have already look at 15 per cent of the possible candidate objects they have in their data, and found about 100 of the objects they called "red transients". Some of them are behaving very dramatically, flaring up to become several thousands times brighter very quickly.
"We are very excited about following up on the 100 red transients we have found", said Beatriz Villarroel in a statement.
They hope to launch a new project that will use citizen science and artificial intelligence to comb through the remaining 150,000 candidates that have already been identified.
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