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Curated by RSF Research Staff

From somewhere … to everywhere!

Atomic Hydrogen (H) - the first element in our periodic table - has given an unexpected and unprecedent apparition. A recent study by Lutz Wisotzki of the Leibniz Institute of Astrophysics in Potsdam and collaborators from different institutions reveals the presence of H all over the sky, including the apparent empty space between galaxies. This was concluded after detecting one of the traits that characterize the H element, and that is part of the digital print of the atom, called "spectrum". We refer to the Lyman-alpha transition of atomic hydrogen at a wavelength of 121.6 nanometres (Ly-α in Figure 1), corresponding to a frequency of 2.47×1015 hertz.

Figure 1: Hydrogen emission spectral series.

The Lyman-alpha line is in the ultraviolet section of the electromagnetic spectrum. Because it is absorbed by air, its astronomical detection must be carried out by satellite-borne instruments, unless the source is extremely far, with redshifts that allow the hydrogen line to penetrate the atmosphere. Such was the case in this study. The instrument behind this observation, MUSE, is located on the Very Large Telescope (VLT) of the European Southern Observatory, Cerro Paranal, Chile. It is designed to detect the distribution of wavelengths from astronomical objects with high sensitivity. As such, instead of looking at a single intense cosmological object, a wide view of very faint signals from the entire cosmos was produced. It also allows researchers to observe signals of galaxies that are too far or too faint to be observed with the Hubble telescope.

It is a mind-expanding realization that almost the whole of the early universe shows a faint glow in the Ly-α line, revealing the cosmic reservoirs of atomic hydrogen for the first time.

This study published in Nature not only reveals the existence of extensive masses of gas all over space, it also confirms the idea that depending on the glasses we wear, we see very different things. In this case, the fundamental element or building block of the universe - the H atom - is not only in stars or in a gaseous form surrounding early galaxies, but it is everywhere!

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