Almost the entire cosmos is filled with a faint glow of hydrogen
Almost the entire cosmos is filled with a faint glow of hydrogen
This even surprises astronomers: the whole sky is filled with a faint glow invisible to our eyes. It comes from huge clouds of hydrogen gas that surround distant galaxies. The researchers only discovered this so-called Lyman alpha emission with the help of an especially sensitive spectrograph, because the brightness of diffuse hydrogen clouds is extremely weak, as astronomers report in the scientific journal "Nature."
Hydrogen is the primordial element of our universe: Shortly after the Big Bang, this gas was present and formed the building material for all the stars and galaxies. To this day, most galaxies are surrounded by hydrogen shells and there are also extensive clouds of this original gas between the stars. It can be recognized by the so-called Lyman-Alpha emission. This radiation is released when the hydrogen atoms are excited by the input of energy and when they return to the ground state they release this energy as UV radiation with a wavelength of 121.6 nanometers.
Deep view in Hubble Ultra Deep Field
But how much of this hydrogen gas is there? And how far do the gas layers of galaxies extend? "Until now little was known about the spatial distribution of this gas," explains Lutz Wisotzki, of the Leibniz Institute of Astrophysics in Potsdam (AIP) and his colleagues. "Because the extremely low brightness of this extended emission makes it extremely difficult to detect.
Only the sensitive MUSE spectrograph in the Very Large Telescope of the European Southern Observatory in Chile makes this possible. The astronomers used it to observe the Hubble Ultra Deep Field (HUDF), an area in the Fornax constellation in which the Hubble space telescope had looked deeper than ever before in space. It contains thousands of distant galaxies scattered in a seemingly dark sky.
Lyman luminaires - almost everywhere
But the UXO data revealed: what previously appeared dark, in fact, is almost completely filled with the faint glow of Lyman's alpha radiation. The hydrogen shells of the distant galaxies were so large that they filled almost the entire field of vision. Projected across the sky, this means: "This emission covers almost 100 percent of the sky," the researchers report.
"That was a surprise that opened his eyes in the true sense of the word," says Wisotzki's colleague, Kasper Borello Schmidt. Because it is the first time that astronomers have been able to make this weak radiation visible from the gas layers of early galaxies. And as it now turns out, its alpha Lyman shine extends far further into space than previously assumed. "This opens a new window to an important but previously invisible part of the cosmic distribution of matter," the researchers explain.
Source of energy still unknown
Although this glow of hydrogen is not visible to us, it is omnipresent: "The next time you look into the moonless sky and see the stars, imagine the invisible glow of hydrogen: the first building block of the universe illuminates the entire night sky with its radiance, "says team member Themiya Nanayakkara of the University of Leiden.
It is not yet clear what causes these distant hydrogen clouds to shine and their exact distribution is still unknown. That's why we want to make even more sensitive measurements in the future, "says Wisotzki. We want to discover how these gigantic deposits of atomic hydrogen are distributed in space ".
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