The launch of the James Webb Space Telescope has allowed astronomers to observe the universe so closely that we are approaching the time when the earliest galaxies are believed to have formed. For most of the history of the universe, there seems to be a consistent correlation between the number of stars a galaxy has produced and the amount of heavy elements it has produced.
But for the first time we now see signs that this relationship between the number of stars and the elements does not exist in the earliest galaxies. The reason is probably that these galaxies are just in the process of formation, and they haven't had time to create the heavy elements yet.
The universe is full of galaxies – vast collections of stars and gas – and when we look deep into the cosmos, we see them near and far. Because it took longer for light to reach us, the more distant a galaxy is, we are actually looking back in time, and this allows us to build a visual narrative of their development throughout the history of the universe.
This diagram shows the galaxies observed in the "elements - stellar mass diagram": the further to the right a galaxy is, the more massive it is, and the higher it is, the more heavy elements it contains. The gray icons represent galaxies in today's universe, while the red ones show new observations of ancient galaxies. These clearly have far fewer heavy elements than later galaxies, but they more or less fit the theoretical predictions, represented by the blue bar.
Observations have shown us that galaxies for the last 12 billion years - that is, 5/6 of the age of the universe - live their lives in a kind of equilibrium: there seems to be a fundamental and close connection between the number of stars they have created on the one hand, and the number of heavy elements they have created on the other hand. In this context, "heavy elements" means anything heavier than hydrogen and helium.
This connection makes sense because the universe originally consisted of only these two elements, the lightest. All the heavier elements, such as carbon, oxygen and iron, were later formed by the stars.
The very first galaxies should therefore be "pure" of heavy elements. But only recently can we look back at such a distant time. In addition to distance, the reason is that the longer light travels through space, the redder it becomes. Regarding the most distant galaxies, we have to look deep into the AA part of the spectrum, and only after the launch of James Webb do we have a telescope large enough and sensitive that can look that far.
And the space telescope did not disappoint: several times James Webb broke his record for the most distant galaxy, and now we seem to be entering an era where some of the earliest galaxies were formed.
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