Astronomers have explained for the first time where the “missing” baryonic matter of the Milky Way may be located. Scientists have developed a method for detecting previously invisible clots of cold gas. The study was published in the journal Monthly Notices of the Royal Astronomical Society.
Most of the mass of the universe, according to current views of the scientists, accounts for the mysterious dark matter and dark energy, and only about five percent – on the “normal” or baryonic matter, which consists of all visible objects – stars, planets, asteroids, and interstellar dust and gas.
But even this relatively small amount of “normal” matter is often undetectable to astrophysicists. For example, for the Milky Way, no more than half of the estimated amount of baryonic matter has been identified to date.
“We suspect that most of the ‘missing’ baryonic matter is in the form of clouds of cold gas either in galaxies or between galaxies,” the first author of the study, graduate student Wang Yuanming (Yuanming Wang) from the School of Physics, quoted in a University of Sydney press release. – This gas cannot be detected using traditional methods, because it does not emit its own visible light and is too cold for radio astronomy.
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Scientists used radio signals from distant flickering galaxies as “locators” to locate cold gas clouds.
“We detected five shimmering radio sources located on a giant line in the sky. Our analysis shows that their light must have passed through the same cold blob of gas,” Wang explains.
Just as visible light is distorted as it passes through Earth’s atmosphere, causing stars to flicker, radio waves also change their intensity as they pass through matter. It is this “flickering” that researchers have discovered.
Scientists don’t yet know what made the cloud they discovered and how it formed, but they have a hypothesis about it.
“We’re not quite sure what this strange cloud is, but we think it’s a ‘snowy’ hydrogen cloud that was destroyed by a nearby star to form a long, thin blob of gas,” says another study author Dr. Artem Tuntsov of Australia’s Manly Astrophysics Institute.
Hydrogen freezes at about minus 260 degrees Celsius and the authors suggest that the missing baryonic matter of the universe is encased in such clouds of frozen hydrogen. Such objects have so far been impossible to detect directly, but now scientists have a new method.
To detect the gas cloud, the authors used data from the CSIRO Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in Western Australia. The wide field of view of this telescope allows us to see tens of thousands of galaxies in a single observation. This made it possible to measure the shape of the gas cloud.
“This is the first time that multiple ‘scintillators’ have been detected behind the same cold gas cloud. In the next few years, we will be able to use similar methods to detect a large number of such gas structures in our Galaxy,” notes Professor Tara Murphy, scientific leader of the study.