Wow! sign – Wikipedia

1977 narrowband radio sign from SETI

The Wow! sign was a robust narrowband radio signal detected on August 15, 1977, by Ohio State University‘s Big Ear radio telescope in america, then used to help the search for extraterrestrial intelligence. The sign appeared to return from the path of the constellation Sagittarius and bore the anticipated hallmarks of extraterrestrial origin.

Astronomer Jerry R. Ehman found the anomaly just a few days later whereas reviewing the recorded knowledge. He was so impressed by the outcome that he circled on the pc printout the studying of the sign’s depth, “6EQUJ5”, and wrote the remark “Wow!” beside it, resulting in the occasion’s extensively used identify.^[2]

The complete sign sequence lasted for the total 72-second window throughout which Large Ear was in a position to observe it, however has not been detected since, regardless of a number of subsequent makes an attempt by Ehman and others. Many hypotheses have been superior on the origin of the emission, together with pure and human-made sources, however none of them adequately clarify the sign.

Though the Wow! sign had no detectable modulation—a way used to transmit info over radio waves—it stays the strongest candidate for an extraterrestrial radio transmission ever detected.^[3]

Background[edit]

In a 1959 paper, Cornell University physicists Philip Morrison and Giuseppe Cocconi had speculated that any extraterrestrial civilization trying to speak by way of radio indicators may achieve this utilizing a frequency of 1420 megahertz (21-centimeter spectral line), which is naturally emitted by hydrogen, the commonest factor within the universe and due to this fact seemingly acquainted to all technologically superior civilizations.^[4]

In 1973, after finishing an in depth survey of extragalactic radio sources, Ohio State College assigned the now-defunct Ohio State University Radio Observatory (nicknamed “Large Ear”) to the scientific search for extraterrestrial intelligence (SETI), within the longest-running program of this sort in historical past.^[5] The radio telescope was situated close to the Perkins Observatory on the campus of Ohio Wesleyan University in Delaware, Ohio.^[6][7]

By 1977, Ehman was working on the SETI undertaking as a volunteer; his job concerned analyzing by hand giant quantities of information processed by an IBM 1130 laptop and recorded on line printer paper. Whereas perusing knowledge collected on August 15 at 22:16 EDT (02:16 UTC), he noticed a sequence of values of sign depth and frequency that left him and his colleagues astonished.^[4]
The occasion was later documented in technical element by the observatory’s director.^[8]

Sign measurement[edit]

The string 6EQUJ5, generally misinterpreted as a message encoded within the radio sign, represents in actual fact the sign’s intensity variation over time, expressed within the specific measuring system adopted for the experiment. The sign itself seemed to be an unmodulated continuous wave, though any modulation with a interval of lower than 10 seconds or longer than 72 seconds wouldn’t have been detectable.^[9][10]

Depth[edit]

The sign depth was measured as signal-to-noise ratio, with the noise (or baseline) averaged over the previous couple of minutes. The sign was sampled for 10 seconds after which processed by the pc, which took 2 seconds. The outcome for every frequency channel was output on the printout as a single alphanumeric character, representing the 10-second common depth, minus the baseline, expressed as a dimensionless a number of of the sign’s standard deviation.^[11]

On this specific depth scale, a space character denoted an depth between 0 and 1, that’s between baseline and one commonplace deviation above it. The numbers 1 to 9 denoted the correspondingly numbered intensities (from 1 to 9); intensities of 10 and above had been indicated by a letter: “A” corresponded to intensities between 10 and 11, “B” to 11 to 12, and so forth. The Wow! sign’s highest measured worth was “U” (an depth between 30 and 31), which is thirty commonplace deviations above background noise.^[2][11]

Frequency[edit]

John Kraus, the director of the observatory, gave a worth of 1420.3556 MHz in a 1994 abstract written for Carl Sagan.^[8] Nevertheless, Ehman in 1998 gave a worth of 1420.4556±0.005 MHz.^[12] That is (50±5 kHz) above the hydrogen line worth (with no red- or blue-shift) of 1420.4058 MHz. If attributable to blue-shift, it might correspond to the supply shifting about 10 km/s (6.2 mi/s) in the direction of Earth.

An evidence of the distinction between Ehman’s worth and Kraus’s may be present in Ehman’s paper. The primary local oscillator within the telescope’s radio receiver was specified to a frequency worth of 1450.4056 MHz. Nevertheless, the college’s buying division made a typographical error within the order kind, as a substitute acquiring an oscillator with frequency 1450.5056 MHz (i.e., 0.1 MHz greater than desired). The software program used within the experiment was then written to regulate for this error. When Ehman computed the frequency of the Wow! sign, he took this error under consideration.^{[citation needed]}

Bandwidth[edit]

The Wow! sign had a bandwidth of lower than 10 kHz. It’s thought-about narrowband emission within the sense that its fractional bandwidth was comparatively small (~1%). Nevertheless, the 10 kHz bandwidth isn’t small in comparison with the bandwidth of some astrophysical masers (~1 kHz) or to the frequency decision of recent narrowband SETI searches (~1 Hz).^[13] The Large Ear telescope was geared up with a receiver able to measuring fifty 10 kHz-wide channels. The output from every channel was represented within the laptop printout as a column of alphanumeric depth values. The Wow! sign is actually confined to 1 column.^[12]

Time variation[edit]

On the time of the statement, the Large Ear radio telescope was solely adjustable for altitude (or peak above the horizon), and relied on the rotation of the Earth to scan throughout the sky. Given the velocity of Earth’s rotation and the spatial width of the telescope’s statement window, the Large Ear may observe any given level for simply 72 seconds.^[14] A steady extraterrestrial sign, due to this fact, could be anticipated to register for precisely 72 seconds, and the recorded depth of such sign would show a gradual enhance for the primary 36 seconds—peaking on the heart of the statement window—after which a gradual lower because the telescope moved away from it. All these traits are current within the Wow! sign.^[15][16]

Celestial location[edit]

The exact location within the sky the place the sign apparently originated is unsure as a result of design of the Big Ear telescope, which featured two feed horns, every receiving a beam from barely totally different instructions, whereas following Earth’s rotation. The Wow! sign was detected in a single beam however not within the different, and the information was processed in such a approach that it’s unimaginable to find out which of the 2 horns acquired the sign.^[17] There are, due to this fact, two attainable right ascension (RA) values for the situation of the sign (expressed beneath when it comes to the 2 primary reference systems):^[18]

	B1950 equinox	J2000 equinox
RA (optimistic horn)	19h22m24.64s ± 5s	19h25m31s ± 10s
RA (damaging horn)	19h25m17.01s ± 5s	19h28m22s ± 10s

In distinction, the declination was unambiguously decided to be as follows:

	B1950 equinox	J2000 equinox
Declination	−27°03′ ± 20′	−26°57′ ± 20′

The galactic coordinates for the optimistic horn are l=11.7°, b=−18.9°, and for the damaging horn l=11.9°, b=−19.5°, each being due to this fact about 19° towards the southeast of the galactic aircraft, and about 24° or 25° east of the Galactic Center. The area of the sky in query lies northwest of the globular cluster M55, within the constellation Sagittarius, roughly 2.5 levels south of the fifth-magnitude star group Chi Sagittarii, and about 3.5 levels south of the aircraft of the ecliptic. The closest simply seen star is Tau Sagittarii.^[19]

Initially, no close by Solar-like stars had been recognized to lie inside the antenna coordinates, though in any path the antenna sample would embody about six distant Solar-like stars as estimated in 2016.^[9] In 2022, a paper printed within the International Journal of Astrobiology recognized three seemingly Solar-like stars inside the antenna-pointed coordinates. The higher characterised star, 2MASS 19281982-2640123, is situated 1,800 mild years away, solely 132 mild years away from Maccone’s estimation the place an clever civilization is extra prone to exist.^[20] The opposite two candidates, 2MASS 19252173-2713537 and 2MASS 19282229-2702492, had been insufficiently characterised however nonetheless prone to be Solar-like stars. Additionally, 14 different catalogued stars on the antenna coordinates should develop into just like the Solar after extra knowledge turns into out there.^[21][22][23] As a response to the invention, Breakthrough Listen performed the primary focused seek for the Wow! Sign in its first collaboration between the Inexperienced Financial institution Telescope and the Allen Telescope Array of the SETI Institute.^[24][25] The observations had been carried out on Could 21, 2022, lasting 1 hour from Greenbank, 35 minutes from ATA, and 9 minutes and 40 seconds concurrently.^[26] No technosignature candidates had been discovered.^[27]

Hypotheses on the sign’s origin[edit]

A lot of hypotheses have been superior as to the supply and nature of the Wow! sign, however none have achieved widespread acceptance. Interstellar scintillation of a weaker continuous signal—related in impact to atmospheric twinkling—may very well be a proof, however that will not exclude the potential of the sign being synthetic in origin. The considerably extra delicate Very Large Array didn’t detect the sign, and the likelihood {that a} sign beneath the detection threshold of the Very Massive Array may very well be detected by the Large Ear attributable to interstellar scintillation is low.^[28] Different hypotheses embrace a rotating lighthouse-like supply, a sign sweeping in frequency, or a one-time burst.^[18]

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Ehman mentioned in 1994: “We must always have seen it once more after we seemed for it 50 instances. One thing suggests it was an Earth-sourced sign that merely acquired mirrored off a chunk of space debris.”^[29] He later considerably recanted his skepticism, after additional analysis confirmed the unrealistic necessities {that a} space-borne reflector would wish to have to supply the noticed sign.^[12]
The sign’s frequency of 1420 MHz can also be a part of a protected spectrum:^[30][31] a frequency vary reserved for astronomical analysis through which terrestrial transmissions are forbidden, though a 2010 examine documented a number of cases of terrestrial sources both interfering from adjoining frequency bands or illegally transmitting inside the spectrum.^[32] In a 1997 paper, Ehman resists “drawing huge conclusions from half-vast knowledge”—acknowledging the chance that the supply could have been navy or in any other case a product of Earth-bound people.^[33] In a 2019 interview with John Michael Godier, Ehman said: “I am satisfied that the Wow! sign actually has the potential of being the primary sign from extraterrestrial intelligence.”^[34]

METI president Douglas Vakoch instructed Die Welt that any putative SETI sign detections have to be replicated for affirmation, and the dearth of such replication for the Wow! sign means it has little credibility.^[35]

Discredited hypotheses[edit]

In 2017, Antonio Paris, Assistant Professor of Astronomy and Astrophysics at St. Petersburg Faculty, Florida,^[36] proposed that the hydrogen cloud surrounding two comets, 266P/Christensen and 335P/Gibbs, now recognized to have been in the identical area of the sky, may have been the supply of the Wow! sign.^[37][38][39] This speculation was dismissed by astronomers, together with members of the unique Large Ear analysis group, because the cited comets weren’t within the beam on the appropriate time. Moreover, comets don’t emit strongly on the frequencies concerned, and there’s no clarification for why a comet could be noticed in a single beam however not within the different.^[40][41][42]

Searches for recurrence of the sign[edit]

A number of makes an attempt had been made by Ehman and different astronomers to recuperate and determine the sign. The sign was anticipated to happen three minutes aside in every of the telescope’s feed horns, however that didn’t occur.^[16] Ehman unsuccessfully looked for recurrences utilizing Large Ear within the months after the detection.^[28]

In 1987 and 1989, Robert H. Gray looked for the occasion utilizing the META array at Oak Ridge Observatory, however didn’t detect it.^{[28][43][page needed]} In a July 1995 take a look at of sign detection software program for use in its upcoming Project Argus, SETI League government director H. Paul Shuch made a number of drift-scan observations of the Wow! sign’s coordinates with a 12-meter radio telescope on the National Radio Astronomy Observatory in Green Bank, West Virginia, additionally reaching a null result.

In 1995 and 1996, Grey once more looked for the sign utilizing the Very Large Array, which is considerably extra delicate than Large Ear.^{[28][43][page needed]} Grey and Simon Ellingsen later looked for recurrences of the occasion in 1999 utilizing the 26-meter radio telescope on the University of Tasmania‘s Mount Pleasant Radio Observatory.^[44] Six 14-hour observations had been made at positions within the neighborhood, however nothing just like the Wow! sign was detected.^{[16][43][page needed]}

Response[edit]

In 2012, on the thirty fifth anniversary of the Wow! sign, Arecibo Observatory beamed a digital stream in the direction of Hipparcos 34511, 33277, and 43587.^[45] The transmission consisted of roughly 10,000 Twitter messages solicited for the aim by the National Geographic Channel, bearing the hashtag “#ChasingUFOs” (a promotion for one of many channel’s TV sequence).^[46] The sponsor additionally included a sequence of video vignettes that includes verbal messages from varied celebrities.^[47]

To extend the likelihood that any extraterrestrial recipients would acknowledge the sign as an intentional communication from one other clever life kind, Arecibo scientists hooked up a repeating-sequence header to every particular person message, and beamed the transmission at roughly 20 instances the ability of probably the most highly effective business radio transmitter.^[46]

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