The chemical precursors of the first galaxies revolutionize our idea of ​​the cosmos

From the point of view of cognitive advances, we live in wonderful times. Recently, SPT0418-47, a young and extremely distant galaxy, was discovered. The light that reaches us from that is distorted to form a ring by the gravitational effect caused by another galaxy interposed between us and SPT0418-47; qThis effect, in addition to introducing a distortion, works as a lens, allowing us to observe a very distant object very well, which would otherwise be poorly visible, and in this specific case increasing the light of the farthest galaxy by 30 times, compared to what would happen in the absence of gravitational lensing. Knowing the laws that give rise to the distortion of the image in question, astronomers in 2020 were able to reconstruct the state of this galaxy in an era corresponding to less than 1.5 billion years after the Big Bang, or when the universe was about 10 percent of current age.

Surprisingly, SPT0418-47 turned out to be already a relatively cold galaxy, and above all well structured and not very chaotic, which contradicts some previous theories according to which all galaxies in the early universe were turbulent and unstable. Not only that: pointing the new James Webb Telescope (JWT) on that same galaxy, earlier this year it was discovered that SPT0418-47 has a small companion, very close to it, but above all that both show the one that in jargon is called a “mature metallicity” – i.e. they already abound in chemical elements such as carbon, oxygen and nitrogen, rather than just helium and hydrogen. Since these chemical elements are formed with nucleosynthesis reactions in celestial bodies which are rather advanced in the evolutionary process called “stellar series”, it follows that at least some galaxies at the beginning of the history of the universe had already seen several generations of stars, despite of their young age, and so they had also advanced along the periodic table, in terms of atomic types produced within them.

Now, exciting new news has arrived: JWT data shows that the dusts of the most studied young galaxy at the moment contain complex carbon molecules, called polycyclic aromatic hydrocarbons, very abundant and surprisingly distributed within SPT0418-47, in the form of large patches dispersed in an uneven way. This discovery has important implications on several levels. Let’s start with the more properly astronomical one: it is known that polycyclic aromatic hydrocarbons are formed near young and massive stars that emit a lot of ultraviolet light. When exposed to this source of energy, as well as in the vicinity of even very cold planetary bodies, where the spontaneous synthesis of even very complex molecules of this type can be observed starting from a few simple precursors, the polycyclic aromatic hydrocarbons gradually become the larger, and as their molecular size increases, the more they tend to form aggregates that eventually resemble particles of smoke or soot floating in space. These hydrocarbon clouds help regulate how gas inside galaxies is heated and cooled, and thus are one of the constraints controlling the formation of new stars.

But there is much more: polycyclic aromatic hydrocarbons, which contain in their chemical structure up to 20 percent of all carbon in the universe they are also one of the most important sources of carbon for the generation of a huge variety of derivative molecules, which can also form in interstellar space, at temperatures close to absolute zero, under the effect of light radiation of the type emitted by the stars in formation to which they are usually close. Under common conditions involving the presence of grains of water ice, polycyclic aromatic hydrocarbons once irradiated give rise to much more complex organic compounds, through reactions of hydrogenation, oxidation and hydroxylation. Among these organic compounds, coincidentally, we find some possible precursors of amino acids and nucleotides, the basic components of proteins, DNA and RNA, which in fact are common in space.

The more we look into the depths of space, the more we discover possible avenues through which an ubiquitous prebiotic chemical may have given rise to what is needed, for the birth of the first Darwinian replicator and the ignition of evolution; but, honestly, the idea that such versatile chemical precursors could be discovered in galaxies so young compared to the beginning of the universe, yet so mature, is a surprise that should amaze anyone. Just think: a huge carbon chemistry laboratory spontaneously set in motion almost immediately after the birth of the universe, operating for billions of years and for an inconceivable vastness, everywhere in the cosmos. Perhaps, after all, the triggering of life was inevitable; in any case, the universe, from a young age, has been an interesting, varied and complex place, far from everything that was thought until the eighties of the past century.