We’ve known for some time that around 95% of the energy content of the universe is in dark matter and dark energy. This dark sector doesn’t interact with light in any way and so is invisible to us with the remaining 5% – the light sector – that represents all of the regular matter in the universe. Yet what if I told you that all of the stars and galaxies and galaxy clusters only comprise 10% of the light sector. The rest has proved as elusive as the dark sector. We think it must exist as an extremely diffuse gas in between the galaxies, yet our intense searches miss up to half of it. At least until now.