How powerful cosmic flashes called FRBs helped scientists detect the hidden ordinary matter spread across the intergalactic medium.
The Puzzle of the Missing Matter
For decades, astronomers have faced a baffling cosmic mystery. While the universe’s total amount of ordinary matter—called baryonic matter, which includes the atoms that make up everything from stars to planets—was accurately calculated through cosmic microwave background studies, nearly half of it seemed to be missing. Galaxies, stars, and gas clouds didn’t account for it all. Scientists knew it had to be out there, but they couldn’t see it.
Now, using a brilliant technique involving one of the most energetic and fleeting phenomena in the universe—Fast Radio Bursts (FRBs)—astronomers have finally tracked down this elusive matter.
What Are Fast Radio Bursts?
FRBs are ultra-powerful flashes of radio waves that last only milliseconds and originate from far-off galaxies. In that blink of time, they can emit more energy than the Sun releases over decades. Despite their intensity, they’re incredibly hard to study because most occur only once and vanish without a trace.
However, their brief appearance belies their value. When these cosmic bursts travel across space, they pass through the gas and plasma that lies between galaxies. This journey changes the signals in measurable ways, offering a unique window into the invisible fabric of the universe.
Shining Light Through Cosmic Fog
As FRBs pass through the intergalactic medium—a vast expanse filled with thin gas and ionized particles—their signals are altered. This change, known as dispersion, stretches the radio waves across different frequencies depending on how much matter they encounter.
By measuring this dispersion and combining it with the known distance to each FRB’s source, astronomers can estimate how much material lies between Earth and the burst’s galaxy. In essence, the FRBs act as cosmic flashlights, exposing the foggy matter that standard telescopes can’t detect.
Pinpointing the Origins of FRBs
To use this method effectively, scientists needed to pinpoint where the FRBs were coming from. Thanks to cutting-edge observatories like Caltech’s Deep Synoptic Array (DSA) and Australia’s ASKAP (Australian Square Kilometre Array Pathfinder), researchers were able to locate FRBs to specific galaxies with great precision.
By studying the paths of eight well-localized FRBs, coming from galaxies as near as 11.7 million light-years to over 9 billion light-years away, they analyzed how much the signals had dispersed. That data provided a direct measurement of how much matter those FRBs passed through on their way to us.
The Big Discovery: Where the Universe’s Matter Hides
The findings were groundbreaking. Scientists discovered that about 76% of all ordinary matter in the universe resides in the intergalactic medium, the thin but expansive gas filling the space between galaxies. Another 15% is trapped in the halos surrounding galaxies—those vast regions of hot gas that extend far beyond the stars. Only 9% is inside galaxies themselves, in stars, dust, and cold gas.
This confirms long-standing predictions made by cosmological simulations, but now, for the first time, these numbers are backed by direct observational evidence.
Why This Matters for Cosmology
Knowing where baryonic matter is located is key to understanding how galaxies form and evolve. It affects everything from how gravity pulls structures together to how stars and planets emerge over billions of years. By mapping this matter, scientists gain a clearer view of the architecture of the universe.
The method also showcases the power of FRBs as a revolutionary tool in astronomy. They’ve gone from mysterious blips to precision instruments capable of charting the unseen.
What’s Next: Thousands More Bursts to Come
With the success of this technique, astronomers are preparing for the next step. Caltech’s upcoming DSA-2000, a radio telescope project set to be operational in the near future, will be able to detect and localize up to 10,000 FRBs each year. This will dramatically increase our ability to map the intergalactic medium with precision and speed.
As more FRBs are discovered and studied, our understanding of cosmic structure will continue to deepen, potentially revealing more secrets of the early universe and how it has changed over time.
Conclusion: Fast Radio Bursts Open a New Cosmic Map
This discovery marks a turning point. Using fast radio bursts, scientists have finally located the universe’s long-lost ordinary matter, bringing clarity to a question that has puzzled researchers for decades. The cosmos is becoming less of a mystery, and with every new FRB detected, we get one step closer to fully understanding the invisible skeleton of the universe.