At the dawn of the universe, astronomers have found an accumulation of cosmic proportions. At least 21 galaxies, forming stars at tremendous speed, merge in the early stages of the formation of a galaxy cluster. And it’s all happening 13 billion light years away – just 770 million years after the Big Bang itself.
This is the earliest protocluster discovered to date, called LAGER-z7OD1, and today it likely evolved into a group of galaxies 3.7 trillion times the mass of the sun.
Such a large protocluster so early in the Universe – hardly a cosmic lightning strike since the curtain on life, the Universe and everything was lifted – could hold some vital clues as to how the original smoke went away and the lights turned on, allowing light to flow freely could flow through space.
Our universe is a vastly interconnected place. Galaxies may seem relatively self-contained, but more than half of all galaxies are gravity bound together in clusters or groups, huge structures of hundreds to thousands of galaxies.
The beginnings of such clusters are not unknown in the early Universe. Protoclusters have been found almost as far away as LAGER-z7OD1, some of them much larger, suggesting that clusters could start assembling much faster than previously thought possible.
But LAGER-z7OD1 is special, according to a team of researchers led by astronomer Weida Hu of the University of Science and Technology of China. It may reveal clues to one of the most mysterious stages in the history of the Universe: the Age of Reionization.
“ The total volume of the ionized bubbles generated by the connected galaxies appears to be comparable to the volume of the protocluster itself, indicating that we are witnessing the fusion of the individual bubbles and that the intergalactic medium in the protocluster is almost completely ionized. is, ”they wrote in their paper.
“LAGER-z7OD1 thus provides a unique natural laboratory to investigate the reionization process.”
Space, you see, wasn’t always the lovely, transparent place it is today. For the first approximately 370 million years, it was filled with a hot, cloudy mist of ionized gas. Light could not travel freely through this mist; it scattered free electrons and that was that.
Once the Universe had cooled sufficiently, protons and electrons began to recombine into neutral hydrogen atoms. This meant that light – not that there was much left – could finally travel through space.
As the first stars and galaxies began to form, their ultraviolet light re-ionized the neutral hydrogen that is ubiquitous in the Universe: first in localized bubbles around the ultraviolet sources, and then in larger and larger regions as the ionized bubbles connected and overlapped, creating the whole spectrum of electromagnetic radiation flows freely.
About 1 billion years after the big bang, the universe was completely reionized. This means that it is more challenging to investigate beyond this point (about 12.8 light years away), but it also means that the reionization process itself is difficult to understand.
Ideally, you need really bright objects whose ionizing radiation could cut through the neutral hydrogen, and that’s what Hu and his team were looking for with the Lyman Alpha galaxies in the Epoch of Reionization survey. These are tiny galaxies from the early Universe that are forming stars at an insane speed, which means that they can be detected at fairly great distances, well within the age of reionization. This makes them useful probes of the period.
During their search, the researchers found LAGER-z7OD1, an overly dense region of galaxies in a three-dimensional space volume measuring 215 million by 98 million by 85 million light years. This volume contained two different sub-protoclusters merging into one larger one, with at least 21 galaxies, 16 of which are attached.
The total volume of ionized space around the galaxies was slightly larger than the volume of LAGER-z7OD1.
“This shows significant overlaps between individual bubbles, indicating that the individual bubbles are in the process of fusing into one or two giant bubbles,” the researchers wrote.
Thus, the protocluster is not only an excellent example of its kind, providing a new data point for studying how these structures form and arise, as well as star formation in the early Universe, it also provides a unique window into the formation and combination of ionized calling in the midst of the age of reionization.
However, what insights will emerge has yet to be discovered. As the researchers note, that will be the work of future, more powerful telescopes that can better perceive the finer details of the reionization process.
The team’s research is published in Nature astronomy.