The wow signal from oseti

Further guessing about the origin of an unknown extraterrestrial laser signal

What if aliens chose bundled light instead of radio signals to carry their interplanetary messages, swearing by the wavelengths in the visible, ultraviolet and infrared range?? Maybe several short laser flashes have already been vying for our attention without us noticing it until now. Australian OSETI (Optical Search for Extraterrestrial Intelligence) astronomer Ragbir Bhathal caught one of these in December 2008 and openly speculates whether it is of artificial origin or its source is a previously unknown astrophysical phenomenon.

The classic wow signal

On 15. August 1977 it looked for a while as if the ather detectives searching for ET and Co. the rough throw succeeded. When young astronomer Jerry Ehman of Ohio State University in Columbus (U.S. state of Ohio) used the Big Ear radio telescope to locate an unusually strong signal that turned out to be an extreme near-band signal pulsating 30 times more strongly than any background noise for 70 seconds at a time, the excitement was raw, especially since the signal apparently moved with the stars. The actual intelligence feature of the pulse was that it switched itself on and off, similar to the sound of a telephone. The probability that the pulsation was of artificial origin was supported by the frequency of the signal. It was at 1420 megahertz, thus just in that radio range, on which "Earthlings" The first stars were not supposed to be sent out of consideration for astronomical research. "It was the most impressive signal we had ever seen", according to Lehman’s recollection of that memorable day. "Without thinking, I wrote on the edge of the computer printout ‘Wow’!"

The wow signal from oseti

Computer printout from 15. August 1977. Picture: Big Ear Radio Observatory

However, all efforts to catch the wow signal a second time were in vain. According to the strict SETI specifications, a suspicious signal should pulsate regularly, be registered by at least a second independent antenna, and also show a recognizable systematic information pattern before it is assigned the attribute "artificial" "extraterrestrial" may decorate, Ehman had to put the heiben candidate on file – until today.

Almost unnoticed and uncommented by the media, 31 years after the legendary wow signal of Ohio, a similar case occurred. Not in the USA, but in Australia. And this time not a radio signal but a laser pulse is in the center of interest. An optical, extremely short laser flash, for which no astrophysical phenomenon known so far is possible, moves the minds of the OSETI community, in particular that of Ragbir Bhathal.

Small historical excursion

Historically, the roots of the OSETI idea go back relatively far, to 1822. At that time, the German mathematician Karl Friedrich Gaub (1781-1849) proposed to transmit the captured and reflected sunlight to the moon or Mars by means of an armada of 100 finely ground mirrors, each of which should have a surface of two square meters. In this way it should be made clear to the Selenites (moon inhabitants) that on their neighboring world intelligent life forms exist, which are interested in good, friendly relations.

Even if similar proposals arose in the course of the 19th century, it was not possible to find a solution. Although the idea of OSETI began to accumulate at the beginning of the twentieth century, it was not until 1960 that the modern idea of OSETI was accepted. It found for the first time a forum in the science magazine "Nature", in which already one year before Morrison and Cocconi had made their legendary SETI plea for a systematic observation of radio waves with powerful scatterers.1

Visibly inspired by this contribution and animated by the first commissioning of a laser (1960), the discoverer of the laser principle, Charles H. Townes, took the leap to the next SETI level.

Townes, who was awarded the Nobel Prize in Physics in 1964 for his discovery of the laser (1959), suggested that the search should not be limited to radio waves alone, but should also be extended to laser flashes and pulses. An advanced civilization, which has undergone a similar technical development as our culture and uses radio waves, should possibly be on our level or even thousands of years more experienced in handling laser technology. It could therefore be inclined to use optical or infrared light for the exchange of interstellar and interplanetary messages. "There is a real chance that we will detect such signals, coming from a society close to our level, with our present telescopes and spectrographs", wrote Townes in 1961.2

The wow signal from oseti

Image: NASA

Although Townes vigorously promoted the OSETI idea throughout his life, his advocacy of the optical search for extraterrestrial light signals provoked remarkably little response, in contrast to the Morrision-Cocconi hype orchestrated by the media. What followed was by no means a lively scientific debate or noteworthy media coverage of his advance. Rather, Townes’ Nature contribution disappeared on the shelves of Western institute and university libraries. "It took the SETI community 30 years to become aware of it", Townes remembers.

The new generation of terrestrial high-energy lasers was the reason why the OSETI idea, which had been temporarily shelved, became fashionable again. In the last two decades, laser technology has made such an enormous leap forward that experts believe it to be the communications and information carrier of the future. It has long outgrown its infancy. No wonder that the optical SETI variant has established itself worldwide as a second pillar of SETI research and has attracted various scientists.

The wow signal from oseti

Dr. Ragbir Bhathal. Image: SETILeague


One of them is Ragbir Bhathal from the University of Western Sydney in Campbelltown (Australia). 60 kilometers from the center of Sydney, he has been leading the only official OSETI project focused on the Sudskies for almost ten years now. Like his colleagues on the other side of the globe, Bhathal uses optical telescopes to search for artificially generated extremely short laser pulses in the visible, ultraviolet and near-infrared range.

Bhathal has been working intensively on OSETI since 1998. In late 2000, during the Sydney Olympics, he ceremoniously launched his first search program, named OZ-OSETI. It is one of several research projects Bhathal oversees in parallel, but by far his grossest passion.

Seconded by two computer-controlled telescopes, coarse in diameter 0.4 and 0.3 meters and located just ten meters apart on campus, Bhathal and his team have since been targeting primarily F-, G- and K-type suns within a 100-light-year radius. At least 1000 stars are concentrated within this region.

stars of F, G and K category could be good mother worlds of terrestrial planets. According to the extrapolations of planet hunters, who have tracked down 353 extrasolar planets so far, some of them should also have nested in the habitable zones of distant stellar systems. Within such a "Grungurtels" can easily conserve water in the liquid state, an essential prerequisite for biological life. And on some of these worlds, intelligent life forms should also exist, some of which in turn seek contact with the stars via laser.

The light detectors mounted on the campus telescopes, known as photomultipliers (PMTs), are highly sensitive. So sensitive that they can easily detect laser pulses that flash for just a billionth of a second (= a nanosecond).

Since also terrestrial lasers can be switched on and off extremely fast and as a result laser pulses of a length up to a trillionth of a second can be created without coarse energy expenditure, the majority of OSETI researchers relies in practice on nanosecond laser pulses in the hunt for aliens. In this process, the light sensors of the telescopes are fully challenged, because everything happens in a time window of only a billionth of a second. This is a very short period of time, in which the light travels just 30 centimeters. In any case, the light detectors of the OSETI hunters have to switch quickly. After all, it is necessary to register all incoming light particles photon by photon. After all, at the nanoscale, every particle of light matters.

While a sun-like star emits 1012 photons per second on one square meter3, the OSETI specialists were able to collect at best 107 photons per second from a sun-like star at a distance of 1000 light years with a professional telescope – based on the statistical average value.4 The light sensors of their telescopes, however, registered at most a handful of photons in the time span of 100 nanoseconds.5

If, on the other hand, ten or more photons in the telescope beam competed within a single nanosecond, this would be a clear indication of an artificial source, especially if the laser signal appeared periodically. If the photons present themselves in a certain interval – independently of how small or coarse this is -, their origin must be artificial nature, because the photons emitted by stars arrive as a rule disordered and without regulated interval.6 On nanosecond basis they can shine with no periodic pattern. A known astrophysical phenomenon or object could by no means generate a particle overshoot on this level and within this time period. Everything spoke for a deliberately pulsed signal of an intelligence.

In their search for the intelligent laser flash, Bhathal and his colleagues from the northern hemisphere follow a technically oriented philosophy: because photons or. Light waves propagate like radio waves at the speed of light, and the wavelength of light is around 500.000 times shorter and conspicuously more tightly bundled, more information can also be accumulated in them and sent quickly. Intelligent civilizations would therefore know that a single photon from the green part of the light would be 500.000 times more energy than a single 21-centimeter radiophoton, because its wavelength is 500 times 000 times shorter. Ragbir Bhathal is therefore certain that aliens prefer lasers as a means of communication:

For an advanced civilization, a technology based on radio waves would be old hat. My feeling tells me that – if there are extraterrestrial intelligences out there – they send us laser pulses or a laser flash.

If they are willing to make contact, they could easily transport huge data packets as a light message across light years through space without loss of information. Packed in high-energy laser beams, the shipment reached the unknown addressee at the speed of light. Once on Earth, our telescopes could then register any near-Earth laser pulse without a terrestrial strobe signal ever having a chance to get in the way.

If ET Co were to use laser pulses to attract attention to themselves, they would have to spread their beam so broadly that it would encompass the entire orbit of the Earth. "If the sender used visible light and a coarse telescope of 10 meters diameter, then they could only aim at stars with at least 2000 light years distance", said the most famous German SETI researcher Sebastian von Hoerner (1919-2003). Only in this way would it be guaranteed that their light message would not be lost in photon-poor space. Finally, a high-energy nanosecond laser pulse emitted by aliens would outshine the home star by many times and would be hard for us to miss.

Bhathal’s wow signal

In the early morning hours of the first week of December 2008, Bhathal’s detectors indeed registered a few photons too many. Since the sensors of the primary telescope worked perfectly and the second campus telescope also confirmed the arrival of the strong signal, the originator of this phenomenon had to be the same "Event", as SETI researchers call a suspicious signal, a strong laser pulse. Had a cosmic neighbor tried to deliver a light-intensive data packet?? In any case, the mysterious signal made Bhathal wonder:

I immediately wondered if ETI was behind it or if it was a false signal or just the source of an unknown astrophysical phenomenon.

At least Bhathal did not completely exclude this possibility. Visibly impressed by the unnaturally strong laser pulse, he noted on the computer printout: "Is it ET?". A good 32 years after Jerry Ehman’s mysterious beacon, which remains unclear to this day, Optical SETI had its first WOW signal.

Bhathal’s way of working resembles that of those colleagues who have dedicated themselves to the natural light of distant worlds. Whenever the weather is good and the sky looks inviting, he points his telescope for a few minutes at a selected star region, collects the data and then moves on to the next one "Target". The data analysis usually follows a day or a few days later.

On the one hand this method should reduce the number of unnecessary false alarms, because two telescopes see more than one, on the other hand it should guarantee that in case of success the stellar origin of a potential signal can be traced back more easily, i.e. the trace can be traced back to the sender directly. But as late as May 2009, Bhathal was still speculating about the origin of his find:

At the moment we are not able to determine the origin of the signal. We are working on it, evaluating all the data several times and trying to exclude all possible natural sources.

Even if the exact astral origin of the pulse remains unknown for the time being, after an intensive research phase of several weeks it became clear that the origin of the signal was in the constellation of Toucan (lat. Tucana7) is to be sought.

But whatever was the source of the short laser flash, whether it came from an optical pulsar or was the product of a completely unknown cosmic phenomenon, may remain forever nebulous, since the nanolaser pulse has not been repeated to this day, and in all likelihood will not be repeated again. Probably for this reason, Bhathal does not give way to the ET thesis, but rather he is reserved:

We are still far from capturing a signal from ET. But if we succeed, this discovery will be even more crude than the discovery of America.

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