After Decades of Searching, We've Finally Found All of the Universe's (Normal) Matter
Right now, 95 percent of all the "stuff" in the universe is still believed to be comprised of dark matter and dark energy, two substances that have never been confirmed to exist, while a large chunk of the remaining 5 percent (the normal or "baryonic" matter) has remained missing.
Last year, astronomers and astrophysicists tracked down the majority of that 5 percent, which was a pretty big coup.
Now, however, an international team claims to have finally found that last chunk of baryonic matter, solving a mystery that has plagued scientists for decades.
"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," said study co-author Michael Shul, from the Department of Astrophysical and Planetary Sciences at the University of Colorado Boulder.
If you looked at how matter (both dark and baryonic) is distributed across the universe, it would look similar to a large web, with stars, galaxies, and black holes concentrated in places where matter is the most dense (and the easiest to observe).
However, matter that's spread across the thinner parts of the web is much harder to observe, making it hard to account for. Scientists have long suspected that the missing baryonic matter would be clouds of gas, but they couldn't confirm their suspicions until now.
When pointed at a quasar, the elusive gas clouds the team had been looking for were finally revealed.
"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," said Harvard-Smithsonian Center for Astrophysics scientist Fabrizio Nicastro, the lead author on the new paper outlining the discovery.
"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."
Now, on to the rest of that 95 percent...