Cosmologists tell us that our universe is made up of 4% ordinary matter, 22% dark matter, and 74% dark energy. The latter two components are “exotic” in that scientists can only speculate regarding their composition or how they originate. While the ordinary matter, consisting of protons, neutrons, and electrons, which we understand, is only a small part of the whole, it also has a dark component. It turns out that about half of the ordinary matter can be accounted for in the stuff we see, like stars and glowing gas and dust. But the other half, probably because it has been too low in density, is unaccounted for. Until now!
Using the European Space Agency’s (ESA) orbiting X-ray observatory called the XMM-Newton, a team of Dutch and German astronomers has discovered part of the missing ordinary dark matter in our universe. In the May issue of Astronomy & Astrophysics Letters, they report observing a filament of hot gas connecting two clusters of galaxies. The existence of this hot gas, with temperatures in the range of 100 thousand to 10 million degrees Celsius, was predicted by astronomers at least 10 years ago as a possible source for the missing ordinary dark matter. Normally such gas would be difficult to detect, but by viewing a bridge of this material linking two clusters of galaxies, Abell 222 and Abell 223 situated about 2.3 billion light-years away, in a somewhat “end-on” fashion, the gas density was high enough to be visible in their instrument.
The authors point out that matter in the universe is distributed in a web-like structure with clusters of galaxies located at the dense nodes of this cosmic web. Prior to this discovery, scientists had suggested that the missing ordinary matter may be found in the filaments joining the nodes. This is exactly what the astronomers observed. Their discovery marks a step toward understanding the distribution of matter within the large-scale structure of the universe.
While the discovery of exotic aspects of our universe carries more public appeal, understanding the makeup and structure of every component is necessary for establishing a credible model. These results support the highly fine-tuned big bang inflationary model for our universe, and add to the growing body of evidence that we are here for a purpose.