'Like trying to see fog in the dark': How strange pulses of energy are helping scientists build the ultimate map of the universe

In early 2024, McGill University doctoral student Vishwangi Shah and her colleagues were conducting a routine review of data from the Canadian Hydrogen Intensity Mapping Experiment when they noticed something strange.

Their analysis traced one of these pulses, known as fast radio bursts (FRBs), to the outer edge of a "dead" galaxy with no new stars. By all logic, that region of space should have been silent. Instead, it was shouting across the universe, sending out hugely energetic waves.

The team was baffled. If their calculations were right, the finding suggested that FRBs may be produced through processes we didn't expect, and far more often than predicted.

They immediately combed through their code, searching for any errors that might explain away the anomaly. When their search came back clean, they realized the implication — they might have stumbled upon a way to solve an unrelated, decades-old cosmic mystery: why a big portion of the universe's "ordinary" matter is missing.

This "normal" matter, called baryonic matter, includes particles like protons and neutrons and other matter that interacts with light, including stars, planets and us. Baryonic matter makes up a small percentage of the universe; the rest comprises mysterious dark energy and dark matter, which are invisible to human eyes.

There should be more ordinary matter in the universe than what we have detected. And the FRB that Shah and her colleagues had detected was a bright, shining beacon pointing to some of that missing matter. As FRBs traverse vast cosmic distances, they can be perceptibly slowed by the presence of baryonic matter — but not by its dark counterpart. Studying these incredibly brief flashes of light, therefore, could be a serendipitous tool for finding the universe's missing matter.

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Now, scientists are doing just that: They're trying to use FRBs to create a map of the universe's matter. What they are learning could reshape what we know about how stars, black holes and galaxies grow over time.

The "missing baryon problem"

Baryons are the class of subatomic particles that includes protons and neutrons, the basic building blocks of atoms, as well as a handful of ultra-rare, exotic particles that are thought to make up a tiny percentage of baryons. Baryons are found in all of the visible matter in the universe but not in the mysterious dark matter that exerts gravitational pull but does not interact with light.

In the 1990s, scientists analyzed the elements created by the Big Bang and calculated that baryonic matter should make up about 5% of the total mass and energy in the universe. This model of the Big Bang, called the Lambda Cold Dark Matter (Lambda-CDM) model, is generally accepted by experts as most likely to represent what happened.

But where is all that matter? Across all planets and stars, scientists can find only around 70% of the baryons they predicted should be in the universe. "It's basically a cosmic bookkeeping problem," Manisha Caleb, an astrophysicist at the University of Sydney, told Live Science in an email. The discrepancy between the amount of baryonic matter astronomers predicted and the amount they could prove exists became known as the "missing baryon problem."

The missing matter was elusive, and more researchers joined the hunt to find it. "It's kind of annoying and embarrassing to be missing much of the normal ordinary matter in the universe," Liam Connor, an astrophysicist at Harvard University who studies this matter, told Live Science.

Astronomers pointed their telescopes at different types of cosmic objects but couldn't find the missing baryons. Many expected the missing matter to be in wisps of hot plasma that are spread thinly between galaxies, Caleb said. Observing this "warm-hot intergalactic medium" is difficult because it is diffuse and emits very little light, rendering it nearly invisible to current observational instruments. "It's like trying to see fog in the dark," Caleb said.

Finding the missing baryons would help support — or rule out — certain models of the Big Bang. That's because the composition of the early universe, specifically the number of baryons, is tied to the abundance of different elements. Models like Lambda-CDM predict the existence of specific amounts of hydrogen, helium and other light elements at the start of the universe, which can still be measured today. Finding a number of baryons that better matches the predicted elemental abundance is a sign their models are more likely to be accurate.

If that matter doesn't exist, however, "it would mean something is wrong with our models," Julian Muñoz, a theoretical cosmologist at The University of Texas at Austin, told Live Science in an email. Therefore, there might be gaps in scientists' understanding of cosmic history.

A new strategy: fast radio bursts

Scientists have been measuring FRBs using radio telescopes since 2007, when Duncan Lorimer, an astronomer at West Virginia University, made the first discovery of an FRB by accident. Every burst is hugely energetic, releasing more energy in a fraction of a second than the sun does over several days.

True to their name, fast radio bursts are quick; most last around a millisecond. Because they are so short-lived and can originate in any part of the sky, FRBs are often detected by chance. This fleeting nature also makes it difficult to pinpoint where FRBs come from, as astronomers usually have, at most, only a few milliseconds to take measurements.

For that reason, FRB research originally focused on finding the origins of the pulses. Most theories suggest that they come from young magnetars, which are highly magnetized neutron stars — the ultradense collapsed cores of massive stars.

Then, Shah's observation, along with an earlier one from 2020, challenged this model. The discovery of errant FRBs galvanized astronomers because it meant there was a new way to hunt for missing matter. How FRBs form is "a big and very interesting puzzle," Lorimer told Live Science.

If Shah's FRB (named 20240209A) comes from a dead galaxy, then perhaps older magnetars could also beam FRBs into the cosmos — meaning some FRBs may be the last gasps of dying stars. An old magnetar, much like a cooling campfire, may seem quiet and unenergetic, but hidden stresses can still ignite a quick spark.

It's also possible that, under the right conditions — perhaps as old stars merge or as matter builds up around a dead star — new magnetars can form in dead galaxies. There would then be many more FRB sources than scientists previously expected.

Even in 2007, Lorimer thought his work might have broader applications. His paper identifying the first FRB alludes to the possibility of using FRBs to probe the warm-hot intergalactic medium, which was tricky to study with the tools available then.

But scientists didn't explicitly propose using FRBs to find baryonic matter until 2013. In a paper published in The Astrophysical Journal Letters, Matthew McQuinn of the University of Washington proposed pinpointing the missing matter by measuring how much an FRB has slowed as it goes past and through matter on its trajectory — called the dispersion measure.

FRBs are uniquely suited to finding baryonic matter. Because of their high energy levels, FRBs also travel long distances, sometimes through the warm-hot intergalactic medium, and are not affected by dark matter because dark matter doesn't interact electromagnetically. "As far as dark matter is concerned, the FRB doesn't exist, and vice versa," Connor told Live Science.

Much of the observable universe's matter, including the warm-hot intergalactic medium, lies in extremely thin, spread-out gas that is nearly invisible to conventional telescopes. FRBs act as beams of electromagnetic energy, like strong flashlights, that pass through these groups of matter, interacting with particles that change the frequency of FRB waves. Sensors on Earth can measure the frequency of those FRB waves once they reach us and, using complicated analysis, scientists can calculate the dispersion measures.

Scientists didn't put this method to the test until 2020, when a team including McQuinn and his international colleagues applied it to real FRB observations. Using 13 robust FRB dispersion measurements, the team created a model of the cosmic structure of the universe. They calculated that baryons account for roughly 5% of total matter and energy, just as past methods predicted, providing a proof of principle that FRBs can be used to unmask missing matter.

This result also revealed that the current number of baryons in the universe has not changed since the Big Bang and reinforced the prevailing Lambda-CDM model.

In June 2025, Connor and his collaborators used FRBs to estimate where all baryons were located. Their calculations suggested that about 76% of all baryons are in the space between galaxies. "We can actually pinpoint where they've been hiding all along," Connor said. "They're in this wispy, diffuse, ionized state in between the galaxies and in a sort of baryon cosmic web, you might call it."

Therefore, the other 24% of baryons must be elsewhere in the universe, they predicted.

"A baryonic Google Maps"

Understanding the distribution of baryonic matter is critical because it has implications for supermassive black holes, stellar evolution and galaxy formation. "If we can pin down where the missing matter is, we can build much better models of everything from how galaxies recycle gas to how elements get spread through the universe," Caleb said.

The distribution of baryonic matter around supermassive black holes could shed light on how the cosmic behemoths at the hearts of distant galaxies self-regulate. Scientists have figured out that "if things get too hot, [the supermassive black hole] cools itself down. If things chill out, it gets hot and starts forming stars or burping gas into the intergalactic medium," Connor explained.

An understanding of this process, widely accepted by experts since the mid-2000s, helps scientists predict how galaxies evolve. But for distant galaxies, it's hard to measure a black hole's heating and cooling. With enough information about the distribution of baryons around a distant galaxy, astronomers can thus make predictions about how the specific galaxy developed and formed stars.

The amount and pattern of the surrounding baryons also inform scientists about how stars form. And because galaxies are made of stars and black holes, understanding how their growth and formation alter baryonic distribution can teach astronomers about how galaxies grow over time, Muñoz said.

The field is limited by the small number of FRBs that have been pinpointed. To determine a burst's origin, scientists use dispersion measures to reveal how far an FRB traveled to get to Earth. Working backward and taking into account the expansion rate of the universe, astronomers can use the distance traveled to find where an FRB came from.

Although astronomers have observed several thousand FRBs, only about 50 have been traced to their origin.

"The next steps are about scale," Caleb said. "We need hundreds — ideally thousands — of well-localised FRBs so we can use them like pins in a cosmic map."

With more of these locations determined, astronomers will be able to statistically analyze the spatial distribution of matter in the universe. These FRBs could tell us where ordinary matter lies, and celestial objects that interact with dark matter, like galaxies, can point to the locations of dark matter. Together, these pieces of information can reveal the underlying, invisible structure of the universe that connects galaxies and determines how they're arranged.

"In 10 to 20 years, I'd love to see a full 3D map of the baryon distribution across the universe, traced out by FRBs — like a baryonic Google Maps" to use in conjunction with knowledge of dark matter, Caleb said. And there's hope for this dream.

Projects like the Canadian Hydrogen Intensity Mapping Experiment (CHIME) and the Deep Synoptic Array 2000 (DSA‑2000) in Nevada are in the midst of building out their FRB detection capabilities. CHIME is developing three telescopes that work together across continents, so as soon as an FRB is detected, all of the telescopes can tune in and help pinpoint it. The DSA‑2000, meanwhile, will survey the entire sky several times with nearly 20 times more antennae than its predecessor, the Deep Synoptic Array-110, to increase measurement sensitivity by decreasing noise in radio observations.

These instruments, when fully operational, are expected to collectively find the origins of more than 10,000 FRBs per year.

"This is just the beginning" of leveraging FRBs to learn more about the universe, Caleb said.

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