The search for extraterrestrial intelligence was only made possible after the discovery of radio waves. Though the radio waves was mathematically predicted initially by Scottish physicist James Clerk Maxwell in 1867, while observing the wavelike properties of light, it was Heinrich Hertz who successfully demonstrated the electromagnetic waves in his laboratory.
You probably be surprised by the fact that there have been many accounts of searches for extraterrestrial intelligence (within the Solar System) even before the 20th century. One such instance, was Nikola Tesla’s popular claim in 1899.
That year, while working in his lab in the Colorado Springs he encountered an unusual signal. He later claimed that the signal has an extraterrestrial origin. Further scrutiny to his claims, however, led researchers to hypothesize that Tesla may have intercepted radio signal which was transmitted by Guglielmo Marconi earlier that year.
The first large scale, dedicated scientific investigation for searching intelligent extraterrestrial lifeforms was initiated in 1960. Since then, we have encountered several mysterious signals and each is more mysterious than the other.
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11. The Judica-Cordiglia Recordings
The Cordiglia Brothers
The Judica-Cordigila brothers are former Italian radio operators, who became popular after they claimed to have captured multiple radio communication signals from secret Soviet space missions throughout the 1960s.
These are mainly distressed signals, dying and burning sounds of cosmonauts, which support the conspiracy theory regarding the deaths of many cosmonauts and the followed cover up by the Soviet space program.
After many scrutinies over the decades, it is almost certain that the signals picked up by the brothers were not from any spacecraft in space but then what was it?
10. FRB 150418
A fast radio burst or FRB, not to be confused by gamma ray burst, is a high energy phenomena with unknown origin exhibited in transient radio pulses. One such FRB’s was detected in 2015 by the Parkes observatory and was then caught by the Australia Telescope Compact Array.
With the help of Subaru telescope, researchers were quickly able to identify the source of this FRB, for the first time ever. However, it soon became disputed. Now radio astronomers have established that the radio emission instead originates from an AGN or active galactic nucleus accompanied by a supermassive black hole. But the uncertainty is still there.
9. Radio Source SHGb02+14a
Screen shot of SETI@home’s distributed computing project
Radio source SHGb02+14 a is one of the strongest candidates in the search for extraterrestrial intelligence. The signal was discovered for the first time in March 2003 by SETI@home. The source is located in a very peculiar region somewhere between the constellation Aries and constellation Pisces, a direction in which there are no observable stars within 1000 light years from the Earth.
The signal was observed for a total of 9 minutes (over 3 times) at 1420 MHz. One of the three frequencies was in the waterhole region, which is generally considered as one of the standard frequencies which can possibly be used by extraterrestrial intelligence to broadcast signals.
There are other features of this candidate that astound astronomers. One such feature is a rapid frequency drift ranging from 8 and 37 hertz/sec. If this drift is caused by Doppler shift phenomenon, then it would indicate that the source planet is spinning 40 times faster than the Earth.
8. Star Signals
Back in 2012, physicist Ermanno F. Borra of the Laval University in Quebec made a bold claim that a laser can be used by an extraterrestrial civilization to perform interstellar communication. According to his theory, if an extraterrestrial civilization points a laser, towards the Earth, we would be able to observe it here with the help of the host star by carefully analyzing its spectrum.
Based on this, he along with his graduate students studied about 2.5 million stars in search of such a signal, which have been cataloged by the Sloan Sky Survey. The study found not one but a total of 234 different stars and most of these have the same spectral class of the Sun. So in other words, Borra and his team, according to themselves has discovered 234 different extraterrestrial civilizations.
As expected, his findings triggered a massive debate among radio astronomers regarding its mere possibility. Many believe that the mysterious signals were actually caused by calibration problems in the telescope.
7. X-radiation from the Perseus Cluster
The central region of Perseus Cluster viewed by Chandra Observatory
The above image is an X Ray shot of the Perseus galaxy cluster. It is one of the largest, most massive objects in the observable universe, containing thousand of galaxies which are surrounded by super hot plasma cloud. It is also the home for very strange radio emissions, the first of which was observed back in 1970.
The radio signal was again picked up by Uhuru X ray satellite confirming the initial sighting. But since its discovery, astronomers were unable to identify its real source or the reason of its occurrence. Nonetheless, scientists have now come up with a hypothesis that these radio signals are coming from NGC 1275, member galaxy of the cluster and is probably caused by a galactic collision.
Journal Reference: doi:10.1038/173818a0
6. Signal From HD 164595
Intensity of radio signal of HD 164595
In 2015, a team of researchers, including Italian mathematician and astronomer Claudio Maccone discovered a strange radio signal for a brief period of time. The signal was coming from the direction of star HD 164595 located in the constellation of Hercules. After studying the signal more closely, the team concluded that it was either caused by interference of radio frequency of the Earth’s atmosphere or due to gravitational lensing of a distant object.
What makes this signal more mysterious is that it was observed only once and by only one telescope. Later observations conducted by researchers at the SETI institute reported that no important signal at that frequency and position was observed.
Read: What is Fermi Paradox? And Where Are the Aliens?
5. Lorimer Burst
The Karl G. Jansky Very Large Array (VLA) Image Courtesy: Flickr
FRB 010724 also known as the Lorimer Burst was the first ever fast radio burst discovered in 2007 by Duncan Lorimer and his student David Narkevic in West Virginia University after analyzing old data sets collected by the Parkes radio dish in Australia. Since 2007, Lorimer Burst has been the center of attraction for radio astronomers.
But in 2017, the researchers were able to identify the source of these mysterious bursts. Surprisingly, it is a star forming dwarf galaxy located about 3 billion light years away from the Earth. Astronomers had previously thought that FRB 010724 originated from rare cataclysmic events; such as the collision of two neutron stars, or supernova explosions, but the repetitive nature of Lorimer Burst later revealed that whatever causing the burst cannot be simply destroyed.
4. FRB 121102
An extremely powerful flare from a neutron star Image Courtesy: NASA/ Chandra X Ray observatory
FRB 121102 is perhaps the most mysterious fast radio bursts recorded till date. It was observed for the first time in 2012 by the Arecibo radio telescope and appeared to be coming from the direction of the constellation of Auriga. Now most FRB’s tend to appear only once and then goes untraceable. But not this particular FRB.
Since 2015, more than thirty radio burst were observed from the same direction, including the first ten recorded bursts. Based on available data, a group of researchers were able to narrow down its source to a young neutron star but it remains controversial.
A new research in 2017, found out that the waves are highly polarized (transverse waves), which could only be possible if they are passing through the hot plasma with a strong magnetic field.
3. The Space Roar
In year 2006, a group of researchers at NASA stumbled upon a massive radio signal of unknown origin. The signal was captured by NASA’s ARCADE radiometer, which was sent in the upper reaches of the atmosphere to listen for obscure radio and heat signals from early stars and galaxies in the universe.
It was about 6 times stronger than anything observed till date and thus named “Space Roar.” After observing the radio source more closely, researchers determine that emissions were neither caused by internal vibration of the early stars or turbulence of our own galaxy. We are still unable to remotely identify the source of this mysterious noise.
Read: How Strong Are Black Holes? | Precise Measurement of Magnetic Field
2. WoW! Signal
A colored copy of the original transcript, taken out in 1977
On August 15, 1977, while reviewing data from the Big Ear radio telescope situated in Ohio State University, astronomer Jerry Ehman discovered a very peculiar anomaly. It was a narrowband signal marked by high intensity variation for a short period of time. After investigation, Ehman was able to roughly pinpoint the origin of the signal, which appeared to be somewhere near the constellation Sagittarius.
The Big Ear was able to observe the signal for exactly 72 seconds and has not been detected till date, despite repetitive attempts by several astronomers since 1980s. Ehman was so impressed with the discovery that he wrote Wow! beside the reading and that’s how this mysterious signal got its name.
1. Mysterious Signals From KIC 8462852
Artist’s concept of Tabby Star or KIC 8462852
KIC 8462852, popularly known as the Tabby’s star is a main sequence star in the constellation Cygnus about 1,280 light years away from the Earth. The star is known for its drastic changes in observed luminosity. Various observations of the star show small dips in its brightness, but in some cases, these dips were huge as much as 22%.
Read: 15 Brightest Stars In The Sky | Based On Apparent Magnitude
Astronomers have also witnessed a drastic increase in its luminosity for a relatively small period of time. These uneven and drastic changes in brightness of the star have led to speculations that an orbiting comet or dust is behind it. But some believe that a huge structure, constructed by a superior civilization to harvest the star’s energy is responsible for these fluctuations. Who knows?
