© Roger Ressmeyer/Corbis : The Parkes telescope: tuned in.
Mysterious radio wave flashes from far outside the galaxy are proving tough for astronomers to explain. Is it pulsars? A spy satellite? Or an alien message?
Bursts of radio waves flashing across the sky seem to follow a mathematical pattern. If the pattern is real, either some strange celestial physics is going on, or the bursts are artificial, produced by human - or alien - technology.
The weird part is that they all fit a pattern that doesn't match what we know about cosmic physics.
To calculate how far the bursts have come, astronomers use a concept called the dispersion measure. Each burst covers a range of radio frequencies, as if the whole FM band were playing the same song. But electrons in space scatter and delay the radiation, so that higher frequency waves make it across space faster than lower frequency waves. The more space the signal crosses, the bigger the difference, or dispersion measure, between the arrival time of high and low frequencies - and the further the signal has travelled.
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