Scientists have discovered the location of the universe’s missing matter – the half of ordinary matter that could not be previously observed, but which scientists knew to exist. Two independent teams of astronomers, one at the Institute of Space Astrophysics (IAS) in Orsay, France and the other from the University of Edinburgh, recently released studies that outline how they uncovered this missing matter and where it may be. Spoiler alert: it isn’t between the cushions of your couch. Both teams concluded that the universe’s previously astray ordinary matter can be located in the filaments of hot dispersed gas between galaxies.
The teams’ work focused on the universe’s ordinary matter, matter composed of protons, neutrons and electrons, as opposed to mysterious dark matter, which make up most of the known universe. Up until these studies were released, we knew approximately how much ordinary matter existed in the universe, but we did not know where this matter was found. Now that it has been accounted for, scientists can feel more confident in their work. “This goes a long way toward showing that many of our ideas of how galaxies form and how structures form over the history of the universe are pretty much correct,” said Ralph Kraft, a professor at Harvard-Smithsonian Center for Astrophysics in Massachusetts.
Although strands of baryon, the ordinary-matter holding gas linking galaxies, were thought to exist, the phenomenon was not observable through X-ray telescopes. To solve this challenge, both teams incorporated the Sunyaev-Zel’dovich effect, which occurs when enduring light from the Big Bang travels through hot gas. This interaction leaves behind markers of the gas that can be captured and studied. Using data from over 1 million pairs of galaxies, both teams discovered that the baryon gas strands were three to six times denser than normal matter in the universe. This breakthrough confirms what scientists have suspected for decades. “Everybody sort of knows that it has to be there,” said Professor Kraft, “but this is the first time that somebody – two different groups, no less – has come up with a definitive detection.”