Little Green Men
Jocelyn Bell found the first pulsar as a graduate student when she noticed an unusual regularity in
signals collected from a radio telescope. One of the possibilities considered initially
was that they might be beacons established by intelligent beings in the distant Universe. Thus, they
were dubbed LGMs (standing for "little green men") by some.
However, as more pulsars were
discovered it became apparent that they did not have the characteristics that one would expect
for such a beacon (for example, they emit in a broad range of frequencies, which would be a very
inefficient use of energy to power a beacon) and the LGM interpretation was discarded.