SCIENTISTS have been left mystified by a radio signal sent from outer space.

The "fast radio burst" (FRB) came from outside our own galaxy - but experts have no idea what caused it.

2 The Australian National Radio Astronomy Observatory telescope at Parkes, New South Wales, Australia Credit: Getty Images

Radio burst FRB 150215 was received on February 15, 2015 by the Parkes Telescope in Australia.

It is the 22nd cosmic signal of its kind.

But after two years, the experts are no closer to finding out exactly what it was - or where it came from.

2 The Search for Extraterrestrial Institute also use the Parkes radio telescope Credit: Getty Images

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Harvard researchers have suggested that these FRB are caused by alien space travel or advanced alien technology.

But according to a study recent study published by Cornell University, scientists are no closer to settling the debate.

"The burst was followed-up with 11 telescopes to search for radio, optical, X-ray, gamma-ray and neutrino emission.

"Neither transient nor variable emission was found to be associated with the burst and no repeat pulses have been observed in 17.25 hours of observing," writes Astronomer Emily Patroff in a study published by Cornell University.

To put it simply, the signal discovery is the equivalent of hearing a loud bang and then turning around and finding nothing.

Stargazers are left without any clues and have no idea of the direction the sound came from.

Since the first discovery in 2007, FRBs have left scientists scratching their heads.

What type of signals are we receiving from outer space? The latest discovery is called a "fast radio burst" or FRB. They are split-second intergalactic "blips" which are picked up by telescopes. We have received 22 FRBs in the past decade. But scientists are no closer to understanding what they are. All we know is that they are coming from outside of the Milky Way.

All we know is that they originate from outside of our own galaxy and that one of the 22 signals repeats.

There's theories that the bursts come from massive neutron stars emitting huge rays, called pulsars.

But there's hope that it could be alien life trying to get in contact.

Alien hunters at the Search for Extraterrestrials Institute (SETI) have been listening for communications for more than a year.

The project is backed by Facebook founder Mark Zuckerberg and Dr Stephen Hawking.

SETI hopes that by keeping an ear out for radio signals, life forms may get in touch.

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