What would you do if you found a radio source from outer space?
No astrophysicist or astronomer would be surprised. Nearly every natural outer space object emits or reflects some sort of radio signal, including the sun. What if the radio source was pulsing on and off? Still, it would not arouse much interest. What if the pulses were constant, with even delays? Now, that might turn some heads. This might seem like fantasy- more akin to something out of a book or movie. However, the truth is that constant pulses have been found. But what could those radio pulses be? Perhaps alien life attempting to communicate with us. Or it might be some sort of navigational beacon for alien space ships. Whatever it is, there must be some way to find out. This article is about the discovery of a constant radio pulse from outer space, and all that transpired.

To seek answers to the questions that for sure will arise in the mind of anyone with such knowledge, one must look back in time to 1967, at the University of Cambridge. At this particular time, professor Antony Hewish and his team of students were completing the creation of a radio telescope specifically designed to look for scintillation, or twinkling, of radio signals coming from quasars¹. He assigned graduate student Jocelyn Bell to analyze the printed readout charts that came from the telescope's computer. She would periodically read through days of printouts, and analyze them.

Little Green Men

One day, Bell noticed something odd. On a printout, there was a type of pulse she had never seen before. Radio telescopes not only pick up cosmic radio waves, but also those of terrestrial² origin. She first thought these were of normal terrestrial origin , such as a clock ticking, or a car starting. However, those had been seen before, and this pattern was new. She dubbed it "Scruff", to signifiy it being meaningless interference.

Bell picked it up again later. She told Hewish about it, and they set up a high-speed recorder. They failed to pick up the signal again for several months. While Bell went away for Christmas, Hewish kept the telescope running. Bell came back and started analyzing the charts from when she was away, and she finally found what she had been looking for. A clear series of rapid pulses, each about 1/3 of a second long, all equal in strength, and with equal spacing of around a second. This behavior had never been seen in nature before. What was it?

Bell and Hewish speculated that the source could be extraterrestrial intelligence³. The "scruff business" was detracting from her time to analyze scintillation in quasars, and she griped about "Little Green Men getting in the way". Bell decided to name the first radio source LGM-1, for Little Green Men 1. She was at that point only half-joking. She told nothing to the public about it for a long time, because she knew it would cause too much excitement, and she had little proof. But finally, it got out.

Hewish's team decided to publish an article in Nature magazine. Once the news got out that strange radio signals had been discovered, all the papers wanted an interview with the discoverer. Once news got out that the discoverer was a woman, all the papers wanted photo shoots with the discoverer. Soon, many articles about the discovery were being printed. Astronomers and astrophysicists around the world saw it. They tried to decipher the layman's language, and they eventually succeeded. Astronomy circles were in an uproar (well, for astronomy circles, anyway), and everyone was trying to discover the exact locations of the sources. New LGMs were being discovered rapidly, although some were just hoaxes. Was it extraterrestrial intelligence after all?

Thinking about these LGMs, Hewish's team took several things into account. A very important fact they took into consideration was the Doppler Effect. The Doppler Effect is when, for example, a train blows its whistle as it is roaring past, the pitch of the whistle changes to the stationary listeners. This effect is called Doppler-Shift. If this signal really was coming from an inhabited planet, it would be orbiting a sun. Its orbit motion around a sun would be causing Doppler-shifting of the radio signal. The pulses would gradually change frequency. This was not the case, as the pulses came at a constant frequency. This ruled out the case of an inhabited planet. Therefore, it was said that the LGMs were not "little green men", but something entirely different.

As it was known that nearly all natural celestial objects emit radio waves, the LGMs might be some sort of natural celestial object. It became apparent a new name must be given to this whole new class of objects, so they were called "pulsars". This was shorthand for "Pulsating Star". At the time, many astronomers around the world were pondering how these pulsars kept time, and were so consistent. Eventually, three main hypotheses⁴ developed, under constant fire from supporters of other hypotheses. They were later dubbed "The Three Clock Hypotheses" because they all explained, in different ways, the accuracy of the timekeeping method.

The Three Clock Hypotheses

The first of these clock hypotheses was the "Binary Spark" hypothesis. The idea was that in a binary system (two stars orbiting each other), if the two stars brushed by each other at high speeds, they would "spark", or transfer energy between each other. If this was the case, it would have produced some radio emission. Also, the mass of the stars would conceal the "sparks" for some time, and would only be seen during two phases of the entire orbital period. Even so, the stars would have to be moving incredibly fast in order to produce such quick pulses. For the stars to move so fast, it was speculated that it would have to be a binary system of white dwarfs, or possibly neutron stars. Neutron stars were purely conjecture at that point in time, and their use called into question the validity of this hypothesis. It was already on flimsy grounds, as no orbital periods had been observed at such high speeds. The second hypothesis also involved a binary system.

The second proposed clock mechanism was the "Binary Lens" hypothesis. Like the "Binary Spark" hypothesis, this involved a binary system. This hypothesis, however, varied in the cause of the radio emission. The two stars, instead of brushing past each other, acted as lenses, their gravity focusing the natural radio emission of the other into a beam (see Fig. 3). Thus, the stars would have rotated together and acted like a lighthouse. When a lighthouse is viewed from a certain angle, it appears to pulse. This is because the beam of light sweeps past the viewer, illuminating the area for a short while. This clock mechanism, like the "Binary Spark", would also have required a very fast orbital period (four seconds at maximum), and would also have required a very small star, such as a white dwarf as mentioned earlier. The third clock hypothesis, however, was a bit different.

The third proposed clock mechanism was the "Rotation" hypothesis. It would have produced the same "lighthouse effect" that was mentioned in the above paragraph. It consisted of a star that was spinning with some sort of spot that emitted radio waves. This clock system would have required the star to rotate quickly, instead of orbiting. This was much more plausible. For this to occur, however, the star must have had to be very small, as compared to a normal star. This was because a large object is spinning, a single spot would take a longer time to rotate around it than a spot of the same size on a smaller object. Therefore, it must have been rotating incredibly fast, but even so, it still must have been very small to allow the spot to rotate 360° so quickly.

These three clock hypotheses were the subject to debate amongst scientific communities. It seemed as if there would be no end to the quarreling. However, two major discoveries proved one theory alone to be valid.

Process of Elimination

During the clock hypothesis debate, in mid-1968, two more pulsars were found. One in the constellation Vela, and one in the Crab Nebula. These were aptly named the Vela Pulsar and the Crab Pulsar. The Crab Pulsar was spinning incredibly fast, at less than one rotation per second. This strained the first and second hypotheses, as orbital periods had never been observed at that speed. It simply was not possible for that to occur with a pair of white dwarfs. The crab pulsar was also embedded in nova remnants. This was not the case with LGMs # 1-4. At this time the debate was raging hot, when a startling fact became apparent: the Crab Pulsar was not spinning as fast as it was when it was first recorded.

This was the final demise of the first and second hypotheses. This is because orbital periods do not slow down over time, they speed up. However, rotation does slow down over time. Therefore, by process of elimination, as well as support from data, it was decided that pulsars were spinning stars.

The discovery of the Crab pulsar also led to greater understanding of the origins of these objects. At the time, it was the fastest pulsar known, and was the only one within nova remnants. This implied that pulsars could have been "born" in the midst of a nova. It could be that pulsars were actually stars that had imploded.

Conclusion

In all this commotion, what happened to their discoverer? Where did Jocelyn Bell go, and what did she think of these happenings? Did she get any awards for her achievement? Well, for one thing, Bell had got married, and was now Jocelyn Bell Burnell. But more importantly, after all this excitement had subsided, Antony Hewish won a Nobel Prize for "his discovery". This upset many people, as Burnell had been a major factor⁵ in the observations, and the discoverer, if not the ultimate identifier.

This must have dismayed her quite a bit. She seemed to take a rebellious stance. She wrote up her thesis paper (which did not mention pulsars at all in the body), and left Cambridge. She later became a professor at the Open University, UK.

What can be learned from pulsars? What uses do they have to us? For one thing, Pulsars can really be used as navigational lighthouses. Pulsars have been applied in numerous ways. The Pioneer 10 spacecraft was launched in 1972, and on it, there was a plaque. The hope in making this plaque was that it would eventually be discovered by an intelligent race like ours. Engraved on this plaque is a picture of the Pioneer 10 spacecraft, coming out of our solar system. It shows the distances, in binary, from our solar system in relation to fourteen different pulsars, and the time between pulses⁶. As I mentioned earlier, pulsars slow down over time, so these pulsing distances would be a bit slower than represented on the plaque. Thus, if smart enough, these beings would be able to figure out where the craft came from, when the craft came from, and what the creators looked like. So, pulsars do help pinpoint locations, just like lighthouses. Also, the well known project, SETI@home⁷ , is now searching for pulsars, to add to the database of over 1500 known pulsars.

In conclusion, many things can be learned. The discovery of pulsars, in reflection, may have shown humankind many things. It has shown what might happen if humankind had actually discovered extraterrestrial intelligence. It has given humanity a glimpse into the death of stars. It will, with luck, someday show extraterrestrial intelligence where we are. Someday, humankind will probably find extraterrestrial intelligence, but until that point, we have to keep looking.

Bibliography

1. Book: Greenstien, George. Frozen Star. New York, New York: Freundlich Books, 1983. 13-31.

2. Book: Kraus, John D. Radio Astronomy. 1966. 2nd ed. Powell, Ohio: Cygnus-Quasar Books, 1986.

3. Book: McDonough, Thomas R. The Search For Extraterrestrial Intelligence. N.p.: Stephen Kippur, 1987.

4. Reference Book Article: Columbia University Press. "pulsar." The Columbia Encyclopedia. 6th ed. Columbia University Press, 2000. p31635. A69221868. InfoTrac. Main Lib., Palo Alto. 16 Jan. 2002.

5. Magazine Article: Zimmerman, Robert. "A Square Dance in Space." Editorial. Astronomy Sept. 2001. A76940106. InfoTrac. Main Lib., Palo Alto. 16 Jan. 2002.

6. Book: Thorne, Kip S. Black Holes & Time Warps: Einstein's Outrageous Legacy. Walbaum: Haddon Craftsmen, Inc., 1994.

7. Web Site: The Planetary Society. Investigating the "Fabric Of The Universe". SETI@home. 9 Jan. 2002.

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