The search for alien life has always been hampered by the enormous noise generated by Earth, making it difficult to separate alien signals from all the local noise.

But a new method for recognising radio signals travelling in interstellar space could narrow the search considerably.

"I think this is one of the biggest advances in radio SETI in a long time," says astrophysicist Andrew Siemion, co-author of a paper describing the technique and director of the Berkeley Centre for the Study of Extraterrestrial Intelligence (SETI).

Radio waves emitted by an alien civilisation living on the far side of the Milky Way would have to travel 100,000 light years through interstellar space to reach Earth.

These radio waves would be scattered when they encounter the turbulent, ionised plasma of interstellar space.

This type of distortion is unique to interstellar space travel and has previously been observed between rapidly rotating stars called pulsars.

This scattering produces a distinctive 'twinkle' called 'diffractive scintillation', where radio waves begin to interact with each other.

Astrophysics PhD candidate Bryan Brzycki, along with Siemion and colleagues in SETI's Breakthrough Listen project, have developed a programme that can pick out radio waves with this interstellar twinkle from the 'proverbial haystack'.

Siemion said: "For the first time, if we have a single signal, we have a technique that allows us to distinguish it from radio frequency interference."

SETI has been scanning the skies for decades, looking for radio waves that can only be produced by alien technology.

From time to time, a strange frequency rises through the white noise of the universe.

At those moments, it's as if researchers have tuned a radio from a noisy frequency to a musical one.

In a very narrow frequency range, there is a clear, continuous signal, as you will see if you graph the signals from an FM radio or the Voyager spacecraft.

Natural phenomena such as lightning, the Sun, pulsars and supernovae cannot produce these narrow signals. They rumble across the sky at much wider frequencies.

But while there is every reason to suspect these signals, most of them are interference created by human interference, such as satellites, mobile phones, Wi-Fi or microwaves.

For example, the origin of SETI's famous 72-second 'Wow!' signal, detected by a radio telescope in Ohio in 1977, is still debated, but some think it came from a comet. It has not been detected since then.

To make sure they are receiving signals from aliens and not from Earth, SETI will search the sky to see where the signal is coming from.

If it comes from several directions, it is probably localised interference from humans. If it comes from a single point in the sky - a single star - it could be a message from aliens.

But it is not enough to say 'maybe' when answering the existential question of whether we are alone in the universe. We need to be quite sure.

The researchers suggest that if there are aliens out there, they are likely to use radio waves for communication because it is efficient to generate these waves and they can travel relatively unimpeded through the atmosphere and interstellar space.

In fact, the researchers write, an advanced alien civilisation would know that "scintillation itself is a message".

Even if none of the original information in the narrow-band radio signal remains intact after a journey through interstellar space, the team concludes: "the mere presence of scintillation will convey the message: 'We are here'."

 

Source: https://www.sciencealert.com/