The cosmos has plenty of terrifying Lovecraftian features, but one of my favourites is the Space Roar. 

There is a loud radio signal, described as a constant hiss, that seems to pervade the cosmos. It is louder than the radio signature of radio galaxies, and it is without explanation.  

It was discovered in 2009 by the team using the ARCADE experiment. The Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission is a great experiment which was design to detect the radio waves emitted by very distant galaxies. Our atmosphere is opaque to radio waves. This is why we can transmit signals to the other side of the planet. Radio waves bounce on the atmosphere when we produce them and off it when coming from space. To circumvent this situation, ARCADE was placed on a high altitude balloon, which took the instrument to 37km, enough to be able to detect the right radio waves. 

The specific radio waves the experiment was looking for belonged to the first stars in the universe. By analysing the waves, we can measure the heating of the primordial universe by its first inhabitants. 

But what they found was the roar. The roar signal is six times more powerful than the expected value from the first galaxies. And NASA excluded all the known sources, including the dust in our galaxy. 

So there is a radio blast, which covers an area of at least 7% of the Sky (that’s what have been mapped by ARCADE), of emitted by something we have never encountered before. And if this is not a good plot point for a horror story I don’t know what is.