Where is the matter of the cosmos?

What is with the missing matter problem, again?

Did we not hear two decades ago that 'missing matter' of the universe is being found? Now it is not or what?

This time it has to do with missing 'normal' matter. You know...protons, neutrons, electrons, all that for normal matter. Is not all accounted for?

A study, by looking and counting, comes up with 'normal' matter is not accounted for by planets, stars, and galaxies. What!

Where else is there to look for normal matter, then?

A published study in June 25, 2025 reports that a team of scientists used "a unique radio technique to complete the census of normal matter in the universe."

"Careful counting accounting indicates that stars contain only 0.5% of the matter in the universe."  "Just 0.03% of the matter is elements other than hydrogen and helium, including carbon and all the building blocks of life."

So, where else to look? Indeed, what else is left? The dark? The large space between galaxies. Called the intergalactic medium. But isn't that vacuum...one atom for every 35 cubic. feet?

This is not easy. The intergalactic medium is very hot, in the millions of degrees. Not much can look through it, difficult for even x-rays. "Hot gas radiates out through the universe at very short x-ray lengths."

So the team tries a novel technique, called "Fast radio bursts". Fairly new to exploration, discovered in 2007.

"Fast  radio bursts are intense blasts of radio waves that can put out as much energy in a millisecond as the sun puts out in three days"

Astronomers from Caltech and Harvard Center for Astrophysics using an array of 110 radio telescopes studied 69 fast radio bursts. They found 76% of the universe's normal matter is in the space between galaxies and 15% in galaxy halos, and the remaining 9% in stars and cold gas in galaxies.

More detail with Chris Impey from "The Conversation", published by Phys.Org

December 4, 2025.