Astronomers Detect a Surprisingly Huge Galactic Birthplace in The Early Universe - ScienceAlert

At least 21 galaxies, forming stars at a tremendous rate, are merging together in the early stages of the formation of a galaxy cluster.

"The total volume of the ionised bubbles generated by its member galaxies is found to be comparable to the volume of the protocluster itself, indicating that we are witnessing the merging of the individual bubbles and that the intergalactic medium within the protocluster is almost fully ionised," they wrote in their paper.

As the first stars and galaxies began to form, their ultraviolet light reionised the neutral hydrogen ubiquitous throughout the Universe: first in localised bubbles around the ultraviolet sources, and then larger and larger areas as the ionised bubbles connected and overlapped, allowing the entire spectrum of electromagnetic radiation to stream freely.

In their search, the researchers found LAGER-z7OD1, an overdense region of galaxies in a three-dimensional volume of space measuring 215 million by 98 million by 85 million light-years.

The total volume of ionised space around the galaxies was slightly larger than the volume of LAGER-z7OD1.

So not only does the protocluster represent an excellent example of its kind, providing a new datapoint for studying how these structures form and emerge, as well as star formation in the early Universe, it offers a one-of-a-kind window into the formation and combination of ionised bubbles in the middle of the Epoch of Reionisation.