Only the most sensitive instruments could have taken this photo that makes our universe look like a light show instead of the void we think it to be. This image was taken by ESO’s Very Large Telescope. As the name implies, the telescope is Very Large in order to take photos with high definition.
The blue spots of light between galaxies are clouds of hydrogen, the smallest element, that is emitting light in the form of Lyman-alpha radiation, though this result was tentatively identified. It is still unknown why these clouds are emitting this radiation.
LAEs (Lyman-Alpha Emitters) are a type of distant galaxy, associated with the very early universe, which emit light somewhere in the ultraviolet part of the spectrum. Other LAEs have been detected prior to ESO’s image, but those were brighter and therefore easier to see.
These hydrogen clouds are the earliest building blocks of the universe and are not very energetic which is why their signal is so weak. We cannot see them glowing with the naked eye, and until now, have not had a ‘pupil’ large enough to collect enough light to see them.
“Realising that the whole sky glows in optical when observing the Lyman-alpha emission from distant clouds of hydrogen was a literally eye-opening surprise,” said Kasper Borello Schmidt, an astronomer who was part of the team that found the result.
These findings create a more detailed picture of early star and galaxy formation. Now that scientists know the precise locations of these hydrogen clouds, they have more tools for a detailed analysis of early-universe galaxy formation.
So, although the night sky appears to be dark, it is actually gently lit by clouds of hydrogen.