UFOs in space: Are explosive sounds from space aliens?

The sounds last only milliseconds but generate as much energy as the Sun in an entire day.

However no one knows what is causing them.

Since March scientists have now heard 16 powerful radio signals - known as fast radio bursts (FRBs) - from space.

Experts only discovered FRBs for the first time in 2007.

But despite discovering nine years ago very little is known about them - even though an estimated 2,000 FRBs fly across the Universe everyday.

EXOTIC: It is now believed the outer-galactic FRBs are coming from 'an exotic object'

It is now believed the outer-galactic FRBs are coming from "an exotic object" such as a neutron star that rotates with such power it emits extremely bright pulses.

Last year UFO expert Nigel Watson said the FRBs could indicate "a vast alien communication network".

He said: "This extraordinary finding either indicates an as yet unknown or unusual astronomical phenomenon, or it could indicate that this is a vast alien communication network, and the universe is teeming with intelligent life forms.

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"Every unusual signal from outer space encourages us to wonder if it is from an alien civilisation.

"Since this signal seems so elusive and hard to interpret then this should be a candidate for further analysis.

"It would be fantastic if this was an alien signal as the knowledge that we are not alone in this vast universe would have a dramatic impact on our perception of our place in the scheme of things."

It comes as UFOs sightings across the world hit 21 this month alone.