(Web Desk) - On Earth, we're constantly detecting signals from deep space.
Many of these radio waves and other forms of electro–magnetic radiation can be attributed to natural phenomena such as pulsars, colliding stars and the sun.
But some, to this day, remain unexplained – and experts say they could be extraterrestrial in origin.
The 'WOW' signal
The most renowned is the famous 'WOW' signal that was first detected in 1977.
At the time, astronomers discovered a mysterious signal beaming from space that was so powerful it prompted astronomer Jerry Ehman to write 'Wow!' on the telescope's readout.
For decades, scientists debated whether the signal could have been an attempt at communication from a distant alien civilisation, as there were no known explanations for it.
Recently, a team of experts re–examined the signal's data with modern techniques and found that it was more than four times stronger than previous estimates. Although scientists believe the signal is likely to have natural origins, they say alien sources can't yet be ruled out.
Dr Hector Socas–Navarro, director of the European Solar Telescope Foundation, told The Daily Mail: 'While aliens aren't completely off the table, it seems that the signal may have originated by a natural astrophysical source.
'Our goal now is to find that source.'
ASKAP J1832–0911
Earlier this year, experts detected a cosmic entity called ASKAP J1832–0911 emitting joint pulses of radio waves and X–rays for two minutes every 44 minutes some 14,700 light–years from Earth.
This was the first time an object like this, called a long–period transient, had been detected emitting X–rays.
Currently, there is no clear explanation for what causes these signals, or why they 'switch on' and 'switch off' at such long, regular and unusual intervals.
Experts admit even their best theories do not account for what they're seeing, as it challenges the rules of physics.
And they said it could mean ASKAP J1832–0911 is an entirely new class of object that humans have never detected before.