Wow! Signal

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Image 1: Scan of the eponymous document by Jerry R. Ehman

The Wow! Signal was a narrowband radio signal that the astrophysicist Jerry R. Ehman recorded as part of a SETI project on the "Big Ear" radio telescope of Ohio State University on August 15, 1977 from the direction of the constellation Sagittarius . The signal is likely due to an object in the solar system.

The signal

Frequency and strength

The signal was significantly stronger than the background noise with 30 times the standard deviation . The bandwidth was less than 10 kHz. Two different values ​​of its frequency were given, 1420.356 MHz (J. D. Kraus, old value) and 1420.456 MHz (J. R. Ehman, revised value), but both very close to the frequency of 1420.405 MHz, which is derived from the hyperfine structure transition of the neutral hydrogen ( hydrogen line ) is generated in the universe . The difference between these two values ​​can be explained by an error in the system that was only discovered and corrected after the signal. Two possible equatorial coordinates were also given: RA = 19 h 22 m 22 s ± 5 s or 19 h 25 m 12 s ± 5 s , as well as both dec. = −27 ° 03 ′ ± 20 ′ (in epoch B1950.0) . This region is located in the constellation Sagittarius , about 2.5 degrees south of the Chi Sagittarii group. Tau Sagittarii is the closest star visible.

Amazed how narrowband the signal was and how much the intensity -profile possible that a localized signal in the used the antenna would produce edged J. R. Ehman on the computer - expression of the character code "6EQUJ5" (the received intensities ascending encoded with the numbers 1 to 9, beyond 9 with the letters A to Z, “Z” → highest intensity) the intensity variation with the pen and wrote the comment “ Wow !” in the margin. This comment became the name of the signal.

Since the "Big Ear" radio telescope was fixed on the sky and therefore moved with the earth's rotation, it can be assumed that an interstellar signal, in contrast to an earth-bound or solar system-bound signal, would first have increased in intensity after 36 seconds Peaked and then weakened again. Since the signal corresponded exactly to this template , the probability that it is actually an interstellar signal is extremely high. However, at that time a further reception window was tracked exactly three minutes after the first window and the signal should have been received three minutes later; But this was not the case.

It has been speculated whether interstellar oscillation of a weaker, continuous signal (an effect similar to the atmospheric twinkling of stars) is a possible explanation (although it would not disprove the signal's artificial origin). However, the signal with the much more sensitive Very Large Array could not be detected either. The probability that a signal below the sensitivity of the Very Large Array will be received by the “Big Ear” radio telescope due to interstellar scintillation is extremely low at less than 10 −40 .

It is unlikely, but possible, that the signal was terrestrial or from an object within the solar system . The signal was measured for 72 seconds and did not appear to be repeated; all subsequent inquiries - by Ehman himself and by others - could no longer locate it. The nature of the signal therefore remains unclear, and so far only a few possibilities can be excluded.

Interpretation of the paper printout

The horizontal lines in Fig. 1 show the received field strengths at intervals of 12 seconds. Receiving took about 10 seconds, the computer needed about 2 seconds for processing. The vertical columns show the reception field strengths in the individual reception channels. There were 50 channels, each with a bandwidth of 10 kHz. Each character on the printout represents the received field strength in a specific 10 kHz channel and a specific 12 second interval. The smoothed field strength relative to the noise in units of the standard deviation was used for coding. This value was represented by an alphanumeric character. A space meant that the current signal was less than 1 standard deviation above noise. Values ​​from 1 to 9 indicated that the signal was over 1 to 9 standard deviations above noise. Even stronger signals (a factor of 10 to 35 above the noise) were represented by the letters A to Z. The letter U corresponds to the interval 30–31. Usually the expression should have a lot of spaces, with occasional low numbers.

The pattern “6EQUJ5” in a vertical column shows a strong, narrow-band increase in the reception field strength. The maximum field strength was 30 standard deviations above the noise.

Change over time

Figure 2: Course of the reception strength over time

Figure 2 shows the characters as a curve, i.e. the course of the reception strength over time. The actual strength of the signal could have been constant, due to the fixed installation of the antenna and the rotation of the earth, the receiving lobe was rotated past the signal. So there had to be a change from very weak to strong to very weak, similar to a bell curve .

"Horizontal" information

The following explanation deals with the vertical columns in Figure 1, especially with the column with the coded sequence of the signal strengths.

Horizontally, from left to right, there are 20 columns next to each other in Figure 1. These represent 20 channels in which signals were received at the same time.

The bandwidth of each channel was 10 kHz. In Figure 1 there are no strong signals in the rest of the channels, only the general weak noise.

Modulation, content possible?

Jerry Ehman discusses in his essay The Big Ear Wow! Signal full details. In one chapter of the document he discusses the question of whether it is possible that the signal contained modulation , i.e. content.

"The answer from Dr. Ehman was: 'Yes, it is possible.' But at that time the receiver was not efficient enough. The computer of the time wasn't either. With the state of the art at that time, a much narrower-band receiver could have been used, namely with a bandwidth of at most 0.5 kHz, and a second computer for the analysis. If the signal contained a modulation, something similar to the one we used in our Arecibo message , we could not determine the content because of our too simple, broadband receiver. "

Possible explanations

As part of the television documentary Die Aliens - Mythos und Truth ( ZDF , 2010), Harald Lesch explained that the Wow! Signal showed all the characteristics of an interstellar communication attempt, but it could also have been a gigantic outbreak of a pulsar .

Antonio Paris, professor of astronomy at St. Petersburg College in Florida, suggests that the signal was of natural origin and could have come from a passing comet within the solar system. According to Paris, the telescope could have registered the trace of a hydrogen cloud from such a comet at the time. These clouds of hydrogen form when a comet approaches the sun. Possible candidates for this event are comets 266P / Christensen and P / 2008 Y2 ( Gibbs ) , which were only discovered in 2006 . On January 25, 2017, the renewed passage of "266P / Christensen" offered a review of his theory. As a result of this observation and comparative studies on other 1420 MHz sources, Paris and his team came to the conclusion that the comet's cloud was the source of the Wow! This hypothesis is rejected by leading astronomers and is considered to be refuted.

Big-ear radio telescope

The Ohio State University Radio Observatory , also just called The Big Ear , was a radio telescope on the grounds of the Ohio Wesleyan University and was part of a SETI search program at the Ohio State University until 1995 . The longest SETI search program to date was carried out on the Big Ear from 1973 to 1995. After almost 40 years of operation, the telescope was dismantled in 1998, the area sold and then used as a golf course .

literature

  • Robert H. Gray: The Elusive Wow: Searching for Extraterrestrial Intelligence. Palmer Square Press, Chicago 2012, ISBN 0-9839584-4-0
  • Jerry R. Ehmann: "Wow!" - A Tantalizing Candidate. In: H. Paul Shuch: Searching for extraterrestrial intelligence - SETI past, present, and future. Springer, Berlin 2011, ISBN 978-3-642-13195-0 , pp. 47-63.

Web links

Commons : Wow! Signal  - collection of images, videos and audio files

Individual evidence

  1. ^ A b Antonio Paris: Hydrogen line observations of cometary spectra at 1420 MHz . (PDF) In: Journal of the Washington Academy of Sciences , 102, April 1, 2017, No. 2; accessed on June 6, 2017.
  2. ↑ “ The signal was very strong (30 sigmas or thirty times the background), and it was narrowbanded (width of 10 kilohertz or less) because it appeared in only one channel. ”In: David W. Swift: SETI pioneers - scientists talk about their search for extraterrestrial intelligence. University of Arizona Press, Tucson 1990, ISBN 0-8165-1119-5 , pp. 13-15, 244
  3. ↑ Historical SETI signal without cosmogram . Telepolis ; accessed on August 15, 2017.
  4. ↑ Jerry R. Ehman: The Computer Printout. In: The Big Ear Wow! Signal. What We Know and Don't Know About It After 20 Years. February 3, 1998, accessed August 16, 2017 .
  5. ↑ Jerry Ehman: Explanation of the Code "6EQUJ5" On the Wow! Computer printout. Retrieved January 1, 2010 (English).
  6. ↑ Jerry R. Ehman: The Big Ear Wow! Signal. What We Know and Don't Know About It After 20 Years. Big Ear Radio Observatory, September 1, 1997, accessed June 6, 2011 .
  7. ↑ Jerry R. Ehman: The Big Ear Wow! Signal. What We Know and Don't Know About It After 20 Years. Big Ear Radio Observatory, September 1, 1997, pp. 21-23 , accessed June 6, 2011 .
  8. ↑ Video The Aliens - Myth and Truth  in the ZDFmediathek , accessed on February 11, 2014. (offline)
  9. ^ Antonio Paris, Evan Davies: Hydrogen Clouds from Comets 266 / P Christensen and P / 2008 Y2 (Gibbs) are Candidates for the Source of the 1977 “WOW” Signal. (PDF) In: Journal of the Washington Academy of Sciences , 100, 2015.
  10. ↑ Jesse Emspak: Famous Wow! signal might have been from comets, not aliens. newscientist.com , January 11, 2016, accessed January 13, 2016 .
  11. ↑ Thomas Trösch: Weltall: Where does the wow signal come from? In: golem.de . January 12, 2016, accessed January 13, 2016 .
  12. ↑ About the Big Ear Radio Telescope bigear.org, accessed November 20, 2010
  13. ↑ Fernando J. Ballesteros: ET talk: how will we communicate with intelligent life on other worlds? Springer, New York 2010, ISBN 978-1-4419-6088-7 , p. 78