50% of the Universe’s Matter Has Been Missing for Ages; Scientists Just Found It

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https://www.popularmechanics.com/space/deep-space/a64503976/missing-matter-hydrogen/?source=nl&utm_source=nl_pop&utm_medium=email&date=042025&utm_campaign=nl02_042025_POP39402783&oo=&user_email=1e7f7a9239bb44f191dc979b8fe5e634e587dfe020b84a653d2040468a8b342b&GID=1e7f7a9239bb44f191dc979b8fe5e634e587dfe020b84a653d2040468a8b342b&utm_term=TEST-%20NEW%20TEST%20-%20Sending%20List%20-%20AM%20180D%20Clicks%2C%20NON%20AM%2090D%20Opens%2C%20Both%20Subbed%20Last%2030D

50% of the Universe’s Matter Has Been Missing for Years. Scientists Just Found It

Mysterious dark matter makes up 85 percent of matter in the universe, and of the remaining 15 percent, scientists couldn’t account for half—until now.

Apr 18, 2025

Chipper says "The fabric of the Universe consists of PAH or 'Polycyclic Atomatic Hydrocarbons' -- search for the paper on this site to learn more"

● Although we’re still searching for observational evidence of dark matter, scientists haven’t been able to account for about 15 percent of the regular matter in the universe with just stars, planets, and other celestial objects.

● A new study by 75 scientists across institutions around the world suggests that this missing matter is actually ionized hydrogen gas surrounding galaxies, which stretches much further than we thought.

● Understanding the location of this gas is vital to producing accurate simulations and understanding the formation and evolution of galaxies.

Now, a new study co-authored by 75 scientists from institutions from around the world claims to have finally solved this missing matter mystery.

By analyzing the images of 7 million galaxies—provided by the Dark Energy Spectroscopic Instrument (DESI), which is a telescope located in Tucson, Arizona—all located within 8 billion light-years of Earth, scientists discovered that the diffuse clouds of ionized hydrogen gas surrounding galaxies account for more matter than we originally believed possible.

In a preprint uploaded to arXiv and awaiting peer review for publishing in the journal Physical Research Letters, the team explains that this gas likely makes up the missing portion of the 15 percent of matter that isn’t dark matter.

When analyzing these millions of luminous red galaxies, the team used Cosmic Microwave Background (CMB) data—the primeval radiation emitted just after the Big Bang—to measure the dimming and brightening caused by scattering radiation in the ionized gas. This scattering process is known as the Sunyaev-Zel’dovich effect.

“The cosmic microwave background is in the back of everything we see in the universe. It’s the edge of the observable universe,” Simone Ferraro, a co-author of the study from Lawrence Berkeley National Laboratory, said in a press statement. “So you can use that as a backlight to see where the gas is.”

The team discovered that centers of black holes are more active than originally thought, which causes the ionized gas surrounding galaxies to be much more diffuse and farther afield than originally believed; in fact, the team’s estimates suggest that this gas stretches five times farther out from the centers of galaxies that previous estimates suggest ...

Astronomers previously believed that supermassive black holes are most active (and therefore classified as Active Galactic Nuclei, or AGN) during galaxy formation But this new data suggests that they could be active at other points in their lifecycle, as well.

“One problem we don’t understand is about AGNs, and one of the hypotheses is that they turn on and off occasionally in what is called a duty cycle,” Boryana Hadzhiyska, a co-author of the study and postdoctoral fellow from the University of California Berkeley, said in a press statement.

New models and simulations of the galaxy formation and evolution will benefit from including this missing piece of the cosmological puzzle in their calculations.

By underestimating this gas expulsion (Chipper says that the gas is PAH) by black holes, astronomers may have been missing insights into some of the theories surrounding dark matter (such as the idea that gas follows dark matter) and the “lumpiness” of the universe.

“Knowing where the gas is has become one of the most serious limiting factors in trying to get cosmology out of current and future surveys. We’ve kind of hit this wall, and this is the right time to address these questions,” Ferraro said. “Once you know where the gas is, you can ask, ‘What’s the consequence for cosmological problems?’”



Lothar Knopp//Getty Images