When astronomers scan the sky with their telescopes, they are only able to see half of the matter that, according to theoretical models, there should be in the Universe. And we are not talking about dark matter, whose very existence is subject to debate and that no one has yet located, but about the baryonic matter, that is, “normal” matter, made up of protons and neutrons and from which the cells are made. planets, stars, and galaxies.
Astronomers, therefore, believe that about half of all conventional matter “up there” remains invisible to us. Something that also happens in our galaxy, the Milky Way, where around 50% of matter is believed to be concentrated in cold, opaque clumps of gas, too dark to be observed by even the most powerful telescopes. It is what is known as the “lost baryonic matter” of the Milky Way. But how to locate it?
In a study just published by Monthly Notices of the Royal Astronomical Society, Yuanming Wang, from the University of Sydney, Australia, and his team, detail the discovery of five distant and “twinkling” galaxies that point to the existence of an unusual cloud of gas in our galaxy. It is the first time that distant galaxies have been used as “bright markers” to locate a part of the lost matter of the Milky Way. For his work, Wang has developed an ingenious method to help locate the missing matter, and thanks to it he has managed to find a stream of cold gas in our galaxy
not detected so far, about 10 light-years distant from Earth. The cloud is about a trillion km long and 10 billion km wide, but collectively it is only about the mass of the Moon.
“We suspected,” says Wang, “that much of the missing baryonic matter is in the form of clouds of cold gas, either within or between galaxies. This gas is undetectable with conventional methods since it does not emit visible light of its own. and it is too cold to be detected by radio astronomy. So astronomers set about looking for distant galaxies, radio sources in the distant background, and studying how they glow. In this way, the researcher continues, “we found five scintillating radio sources in a gigantic line in the sky. And our analysis shows that their light must have passed through that cloud of cold gas.
In the same way that visible light is distorted when it passes through our atmosphere to give rise to the twinkling of stars, radio waves when passing through matter, are also affected by their brightness. And it was that “galactic twinkle” that Wang and his colleagues detected in their instruments. In the words of Artem Tunstov, a co-author of the research, “we are not quite sure what this strange cloud is made of, but one possibility is that it could be a hydrogen” snow cloud “, distorted by a nearby star to form a long and thin lump of gas.
Hydrogen, in effect, freezes at around minus 260 degrees, and theorists have proposed that some of the baryonic matter lost from the Universe could be “encased” in these “hydrogen snowballs”, almost impossible to detect directly. Despite this, Wang continues, “we now have a method to identify these invisible cold gas clumps using background galaxies as markers. According to Tara Murphy, another of the authors of the article, “this is the first time that multiple ‘sparklers’ have been detected behind the same cold gas cloud. In the next few years, we should be able to use similar methods to detect a large number of gas structures of this type in our galaxy.