Cosmic collision reveals evidence of missing matter in the Universe

A collision between some of the greatest structures in space has given scientists a clue about one of the greatest mysteries in the universe: the location of missing matter. When studying mergers of two galaxy clusters called Abell 98, scientists found a gas filament corresponding to the so-called warm-hot intergalactic medium (WHIM). This plasma fog existing between galaxies turns out to be one of the leading candidates for the place of baryonic matter deficiency in the local universe.

Merger of Abell clusters 98. Photo: NASA/CXC/CfA/A

Missing matter is one of the strangest questions we don’t  have an answer to about the universe yet. We were only able to more or less find out the distribution of ordinary (baryonic) matter in space, which makes up everything we see: stars, planets, galaxies, clouds of gas, intergalactic dust. But recent studies show that on the scale of the Universe, baryonic matter is only about 5%, and the rest fall on dark matter (27%) and dark energy (68%), the nature of which is not yet understood.

Scientists know how much baryonic matter was formed during the Big Bang, thanks to the radiation left over from that era, which is produced through the cosmic microwave background. However, when scientists began to analyze the section of baryonic matter in the modern universe, the numbers did not match. Matter seems to have disappeared somewhere, and this is from half to a third of what is provided for.

One of the possible places where the missing matter can be stored is WHIM — intergalactic gas filaments with temperatures from 10 thousand to 10 million Kelvin, in which baryons are heated and compressed. However, it was difficult to find these hyperfine structures in outer space between much brighter galaxies.

Key to a puzzle

Abell 98 is a cluster of galaxies at a distance of about 1.4 billion light-years from us. X-ray observations of Abell 98 revealed hot gas structures between the two clusters. In early 2022, scientists at the Harvard-Smithsonian Center for Astrophysics published an analysis that found that the intergalactic filament contains a giant shock wave formed from the compression of two superclusters. The analysis also revealed two distinct temperature regimes: one at 20 million Kelvin, and the second at 10 million Kelvin.

“These measurements provide tantalizing evidence of the presence of a larger-scale structure, where the diffuse WHIM connects to the vicinity of the cluster along cosmic filaments,” the scientists explain.

So far, scientists have not been able to find enough WHIM to explain all the missing baryons. But the finding suggests that some of them may be hiding in gas filaments stretching between galaxies or hiding in the form of clouds of thin gas in intergalactic space. 

Earlier we reported on the TOP 5 unsolved mysteries of modern physics.

According to The Astrophysical Journal Letters

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