There is a paradox in the universe: scientists believe that there are millions more giant black holes in the universe than we know about, and yet, if they are there, how would they remain hidden? It turns out they do so by hiding in something almost unbelievably common.

They’ve been hiding in the clouds. Not just regular clouds, though—superdense layers of cloud and gas so heavy that only X-rays can escape. Which is why, by pointing NASA’s NuSTAR X-Ray telescope into those clouds, researchers in the UK’s Durham University were able to confirm something they had previously only suspected: Behind that incredibly dense layer of clouds and gas were five incredibly active, supermassive black holes... and they think those five were only the beginning.

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Of course, sometimes a cloud is just a cloud, not a black hole hiding place. Of the nine dense clouds that astronomers suspected might be hiding a black hole at their center, only five delivered. The other four were merely clouds in a very cloudy universe.

Image: Hubble picture of one of the clouded over black holes / Hubble Legacy Archive, NASA, ESA., next to an artist’s concept of the black hole, minus the clouds / NASA, ESA.