We thought we knew what “normal” matter was—stars, galaxies, planets, and interstellar gas. What physicists call baryonic matter. But when they tried to count it all up… they couldn’t find most of it. Literally half of the stuff they thought should be there was just… gone.
Until now. And oddly enough, the clue came from a strange kind of cosmic blink called a Fast Radio Burst, or FRB.
Imagine a beam of radio light that lasts a few milliseconds and travels billions of light-years. That’s an FRB. At first, they just seemed like weird blips from the deep sky. But scientists noticed something: the farther an FRB traveled, the more its signal slowed down. That small delay meant it was moving through something—something we couldn’t see.
That “something” turned out to be the key to finding the universe’s lost matter.
How a cosmic flashlight revealed the invisible
Using FRBs as cosmic probes, scientists from Caltech and the Harvard-Smithsonian Center for Astrophysics did something remarkable. They used 69 FRBs, including FRB202X-13, one of the most distant ever recorded—from 9.1 billion light-years away—to measure the stuff floating between galaxies.
The signal data came in part from the Deep Synoptic Array-110, a powerful telescope array located in California, and other observatories around the world.
And that’s when everything clicked.
It turns out, 76% of the universe’s baryonic matter—the missing matter—wasn’t inside galaxies at all. It was floating silently in the intergalactic medium, as ionized gas, scattered between one galaxy and the next.
This matched what simulations had predicted for years—but nobody could actually see it until now. As one scientist put it, we’d been seeing only the shadow of matter. But now, the light from these FRBs gave us a way to see the real thing.
What the universe is really made of
Here’s how the numbers break down:
- 76% of baryonic matter is in the intergalactic medium
- 15% exists in hot gas halos around galaxies
- Only a tiny fraction is in the stars, planets, and cool gas that make up galaxies themselves
That’s wild. Most of the “normal” matter in the universe—the kind we’re made of—is just drifting between galaxies, invisible until now.
And this matters. Because once you know where the matter is, you can start answering bigger questions:
How do galaxies actually form? How does light travel through billions of light-years of space? What role do cosmic events—like a supernova or a black hole—play in shaping the stuff around them?
Even more intriguingly, it might help us understand the neutrino—one of the strangest, most ghost-like particles in physics. If we can track how ordinary matter behaves across the universe, maybe we’ll get closer to understanding the particles that almost never interact with anything… but might hold clues to new physics.
What comes next: thousands of new clues every year
And this is just the beginning.
A new project called the DSA-2000 is now being built. It’s expected to detect up to 10,000 FRBs per year, which means we’ll soon be able to build an actual map of the cosmic web that connects everything in the universe. Not just a theory. A real, measurable map of the stuff between galaxies.
And it doesn’t stop there. The James Webb Space Telescope just found over 800,000 galaxies in deep space. Pair that with FRBs, and we’re talking about a whole new view of the universe—one where we’re finally able to fill in the blank spaces between the stars.
For years, we thought we were missing something. Now we know—it was there all along. We just needed the right tools.