The "Wow!" Signal: More Questions Than Answers

Imagine the scene: it is 15 August 1977, Jerry R. Ehman, an astronomer at Ohio State University's "Big Ear" radio telescope is looking carefully over a long sheet of paper. The paper is full of numbers and letters that represent data gathered from the radio telescope, processed by computer and then printed out. To many of us, these numbers and letters would look completely non-sensical. But Jerry Ehman knows just what to look for. He is scanning a printout from the same day, when the "Big Ear" had been pointed towards a tiny section of the constellation Sagittarius. It can be dull and hard work. Scanning thousands of lines listing a radio signals strength at 12 second intervals in 50 frequencies. Background level signals are represented by blanks; stronger ones by numerals or letters. Even though the work is anything but glamorous-the possible payoff would be incredible. The first known alien communication beamed to humanity. Ehman is suddenly startled to see a strong 72 second signal that appears on the printout as 6EQUJ5. Each character represents the strength of the signal over the course of that 12 second period of time.

For example a '5' would mean the signal is five times the background level. When the signal goes above 10 times the background level, it's represented by a capital letter. In their chart the letter 'A' would stand for 10 times the background level and 'U' thirty times. Whatever this was-it was one powerful signal. In fact, Ehman was astonished. The 15 August signal from Sagittarius was the strongest signal the Search for Extraterrestrial Intelligence (SETI) had recorded so far. In his amazement, Ehman wrote "Wow!" in the margin and circled the numbers and letters to highlight them. Thirty-two years later, Ehman's discovery, now known as the "Wow!" signal (for obvious reasons) is just as big a mystery as it was in 1977. Could it have been the 'Holy Grail' of SETI-extraterrestrial communication? Could an orbiting satellite have generated the signal? Perhaps it was a natural astronomical event? Today Jerry Ehman himself says, "There's just not enough information to pin it down." This isn't from a lack of trying either. The first step Ehman took back then was to look through the printout to see if the signal had repeated. The telescope had been aimed so that it scanned the same patch of sky every 24 hours.

If the signal was repeating-and then maybe artificial, it would appear on the paper day after day. Sadly it didn't. Apparently this was a one-time only event. Even more interesting, the telescope monitored two sections of the sky, one behind the other and about two-thirds of a degree apart. This means that the signal should have appeared twice; as each viewing angle brought it into view. However, it didn't. Could an extraterrestrial civilization have beamed a short, high-intensity burst at us and then lost all interest? Probably unlikely, if the civilization had been there to begin with. Could the Earth have briefly passed in front of a beam an extraterrestrial civilization had directed somewhere else? A possible explanation is that a local source caused the signal-an artificial satellite, or from some object in our own Solar System. A fact about this signal that may provide some hopeful clues-should it even reappear again is that the signal occupied only a narrow bandwidth centered on 1420 Megahertz. Many astronomers and exobiologists think that any possible alien life out there would broadcast on this frequency because it is the radio signal generated by the most common element in the universe-hydrogen.

This frequency was off-limits to both terrestrial and satellite transmission. Even if a satellite was in violation of this rule, no known satellites were located in that position of the sky. One other idea is that it was the reflection of terrestrial radio waves that had bounced off a piece of space junk. This explanation also falls flat, because once again the frequency was not supposed to be in use on Earth. Calculations were also done that showed such a strong reflection could not have happened if the space junk was tumbling this way and that, which is typically the case. Another item of interest: the sign of a steady rise and fall as it crossed the radio telescopes field of view indicated a source much further away in space. If this was not the case orbital motion would have taken it out of view before the standard 72 second scanning window had ended. An exotic explanation is a phenomenon known as gravitational lensing. This happens when an object of large mass (black hole, galaxy, neutron star,etcetera) lies between Earth and the source of the signal. This intensifies the normal radio emissions of stars. This event could produce a strong enough signal, but it should have repeated a few times-at the very least until the motions of the Earth, Sun, and the star where it originated overcame the lensing effect. The fact of the matter is, that no one to this day has offered a conclusive explanation of the "Wow!" signal, and it has never been detected again, despite astronomers looking for it in the same region of the sky many times since then.

Seth Shostak, senior astronomer at the SETI Institute in Mountain View, California says: "Nobody's going to believe a SETI signal you find only once. One possibility is it was ET, and in the meantime he's gone on holiday. The other is that it was some kind of interfererence. We're never going to know." The only event in the history of radio astronomy that comes close to this was the first observation of a pulsar signal in 1967. A pulsar is an extremely small (smaller than a city on earth in diameter) and incredibly dense (a cubic centimeter weighs 1,000 tons!) neutron star which rotates, and like a lighthouse, flashes its beam of energy with an intense narrow beam of radio waves.

A neutron star which becomes a pulsar is created when a star at the end of its life and more massive than the sun is at the 'supergiant' stage of its development. Some of these stars such as Betelgeuse can have diameters of almost one billion kilometers and a brightness of 10,000 of our suns. The outer layers of these stars are not very dense at all and they have a relatively cool atmosphere. Beneath this cool atomosphere the first layer of gas, at about 3 million to 10 million degrees centigrade burns hydrogen and turns it into helium. Below that, helium at over 500 million degrees centigrade is converted into oxygen, carbon and nitrogen. Closer to the core of the star where the temperatures reach over one billion degrees centigrade, sodium, neon, magnesium, sulphur, calcium, silver, nickel and silicon are fused into each other at the progressively higher densities and temperatures. Finally at the dead center of the star atoms of iron are created from the last by-product of nuclear fusion-silicon. Once the supergiant star is at this stage is has just a few days to live. The cause of this is that iron is the dead end of the fusion process. This means that it just builds up in the core and doesn't produce any energy to counteract the force of gravity that tries to compress the star from the time of its birth.

For the last time the core of the star collapses. The state of the material in the core of the star before the final collapse is very hard to imagine. The gas is heated to 10 billion degrees centigrade and the density of this material is more than 1,000 tons per cubic centimeter! Within the atoms, the last of the natural barriers formed by the forces of repulsion fall one by one. Electrons are crushed into the nuclei of atoms, where they combine with protons, which are them immediately converted into neutrons-thus neutron star. The gas with the stars core becomes a fluid of particles, all crushed together with incredible density. There is nowhere in the universe where there is a denser or hotter region than the core of a supergiant star that is imploding. The density of the center reaches 10 to the 15th power or one billion tons per cubic centimeter, and the temperature reaches 150 billion degrees centigrade!

When pulsars were first discovered, many thought that they were extraterrestrial civilizations beaming data out into space. The reason for this was that no natural phenomenon had ever been observed in the heavens which pulsed with such huge amounts of energy in such incredibly short and regular periods. We now know that this is because some pulsars spin up to thousands of times a second. Twenty years after the "Wow!" signal in 1997, astronomers at the Green Bank telescope in West Virginia picked up another signal that seemed to be extraterrestrial in origin. This turned out to be just a run of the mill orbiting satellite. Even though techniques had greatly improved since 1977 it still took sixteen hours to figure out the real source of the signal. Seth Shostak says, "It was a very beneficial false alarm because it showed us what might happen in the case of a real detection. It takes a long time to be sure. And in all that time, the media are very interested. There's no secrecy." Science fiction author Robert Sawyer, whose novel, Rollback, talks about the discovery of a definite alien signal, makes the observation that even though we've been listening for 50 years, that's not a long enough time to answer the question of extraterrestrial communication. Says Sawyer, "I suspect that if we continue for a few more decades, we will either find something that leaves the "Wow!" signal totally forgotten, or we will have to face up to something equally astonishing: that we are alone."

However the question is answered, I cannot imagine the excitement and wonder that Jerry Ehman must have felt for a time in August of 1977! A link to wikipedia's entry on the "Wow!" signal here . The top image is of the original printout that Jerry Ehman was looking over on that night with his writing "Wow!" and highlighting of the actual signal and the second image is of the signal's location in the sky in the contellation of Sagittarius. Peace and be well to anyone stopping by!