Little Green Men
In July 1967, a novel long-wavelength radio telescope, the largest of its time, began operations at the Mullard Radio Astronomy Observatory in Lord's Bridge, Cambridgeshire, U.K.
Antony Hewish built the array to study radio emissions from quasars, a very distant, energetic and utterly mysterious newly discovered class of object (today we know they are the black hole powered cores of active galaxies). Graduate student Jocelyn Bell took home a 98-foot long paper strip chart of the telescope's observations (this was a time before microcomputers and wide use of digital data processing and storage by astronomers).
VIDEOS: Aliens and Other Space Mysteries
While marking up the chart in her attic, she noticed a peculiar source that was flickering like a police car strobe light. As any good scientist would do, she checked for instrument noise, malfunction or man made clutter. (In 1963 the all-sky glow of the cosmic microwave background was first suspected to be radio contamination from pigeon droppings in a radio communications antenna.)
Bell realized that the source moved with the Earth's rotation. The source really is in the sky and somewhere out there in the galaxy!
The telescope's builder, Hewish, was intrigued and installed a faster strip recorder. The ghostly source reappeared in On Nov. 28 and the astronomers recorded pulses that lasted a fraction of a second but recurred precisely every 1.3 seconds. The eye-opener was that the pulses were so short in duration that they had be coming from something smaller than a few thousand miles across. This might place the source on an Earth-sized planet rather than a star!
What's more, the unusually narrow frequency of the signal mimicked the signature of man made radar transmissions.
In the absence of a physical explanation, the astronomers toyed with the possibility that the signal could be coming from an alien civilization.
The planet hypothesis was easily testable. If the source was orbiting a star, the signals should show a rhythmic frequency shift as the planet approached and then receded from us along a racetrack orbit. This is the high water mark in the team's taking the E.T. hypothesis seriously. As far back as September, the phenomenon was nicknamed LGM for Little Green Men (just as spurious mechanical malfunctions are dismissed as "gremlins").
ANALYSIS: Space Invaders Unlikely - For Now
What if a planet's motion was detected? Should the British government be alerted to hold a press conference announcing something so momentous as an "hello" from space aliens? Or should the data be trashed in favor of protecting Earth from being tempted to talk to E.T.? What if a hostile, invading civilization was "fishing" across interstellar space for a response to their beacon?
By the end of December, the LGM hypothesis quickly evaporated after astronomers learned the source is not orbiting anything.
The final nail in the coffin came when a second, and then a third pulsating source was found in December. It is very improbable that civilizations at three different stars widely separated in space and time should be simultaneously targeting us at exactly the same radio frequencies.
Finally, in February 1968, Hewish published a paper in the journal Nature that described the phenomena as a signal from a neutron star - the crushed remnant of a massive star.
The details of the mechanism were not then known - only later astrophysicists described the signal as being a rotating beacon of radiation from the whirling neutron star, or pulsar.
In late 1968, a different team identified the pulsar as being in the center of the Crab Nebula, a supernova remnant (shown at top).