Universe’s ‘Missing’ Third Of Ordinary Matter Found In Intergalactic Cosmic Web Filaments

Scientists have finally managed to pinpoint the location of all the ordinary matter in the universe, even though it is spread out, quite literally, all over the place. Before the discovery of this evidence, almost one-third of all ordinary matter — called baryonic matter — was considered “missing.”

Baryonic matter is what makes up everything we can touch and see, (which is only about 5 percent of everything that exists in the universe, the remainder being the mysterious dark matter and dark energy) from the smallest atoms to the largest stars and galaxies, and according to theories around the Big Bang, a certain amount of it was created at the time the universe came into existence. However, observations of the universe showed only about 70 percent of that matter in present day, leading astrophysicists to the “missing baryon problem.”

That missing matter has now been located in the intergalactic filaments of the cosmic web that connects the structures in the universe. Using observations of a quasar called 1ES 1553 (quasars are black holes at the centers of galaxies that are actively consuming material and ejecting massive volumes of gas, making them among the brightest objects in space) with the Hubble Space Telescope’s Cosmic Origins Spectrograph instrument, and then following up with European Space Agency’s (ESA) X-ray Multi-Mirror Mission (XMM-Newton) satellite, they found the filaments to contain signatures of oxygen gas, heated to about 1 million degrees Celsius.

“After combing through the data, we succeeded at finding the signature of oxygen in the hot intergalactic gas between us and the distant quasar, at two different locations along the line of sight. This is happening because there are huge reservoirs of material — including oxygen — lying there, and just in the amount we were expecting, so we finally can close the gap in the baryon budget of the Universe,” Fabrizio Nicastro, of the Italian Istituto Nazionale di Astrofisica (INAF)—Osservatorio Astronomico di Roma and the Harvard-Smithsonian Center for Astrophysics, who was lead author of the paper about the discovery, said Wednesday in an ESA statement.

The density of baryons found by researchers, when extrapolated to the entire universe, accounts for about 30 percent of ordinary matter. Of the rest, only about 10 percent lies in all the galaxies in the universe, including all the countless stars and planets within them, as well as the interstellar gas that stars form from. Another 60 percent or so is found in the diffuse clouds of gas that fill up the large distances between galaxies.

However, galaxies and galaxy clusters, held together by gravity, are the densest parts of the universal network of filaments that is the cosmic web, and are few and far between. Therefore, astronomers had to look beyond, to intergalactic medium, to find the rest.

In 2012, Michael Shull and Charles Danforth, from the University of Colorado, Boulder, suggested where the erstwhile missing baryons could be found. They were also coauthors on the new paper. In a statement by the university, Shull said the finding also validated the Big Bang theory.

“This is one of the key pillars of testing the Big Bang theory: figuring out the baryon census of hydrogen and helium and everything else in the periodic table,” Shull said, adding that the findings needed to be confirmed by observing more quasars.

The paper, titled “Observations of the missing baryons in the warm–hot intergalactic medium,” appeared online Wednesday in the journal Nature.