Researchers from Edinburgh University believe alien races could have used the gravity of stars to 'slingshot' probes in order to gain speed: a technique humans already use for probes, such as the Voyager.
The Voyager space probe uses a 'slingshot' technique but uses planets rather than stars as the Scotland-based mathematicians suggest, 'The Independent' reported.
The researchers also analysed how a fleet of probes could 'self replicate' and build new versions of themselves from dust and gas while travelling through space.
"The fact we haven't seen probes of this type makes it difficult to believe that probe building civilisations have existed in the Milky Way in the last few million years," Forgan said.
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According to the researchers' calculations, alien probes would only need to travel at one tenth of the speed of light in order to explore every part of our galaxy within 10 million years.
"We can conclude that a fleet of self-replicating probes can indeed explore the Galaxy in a sufficiently short time...Orders of magnitude less than the age of the Earth," researchers concluded.