For decades, a cosmic mystery has puzzled scientists: the whereabouts of the universe's missing baryonic matter. This "ordinary" matter, composed of protons, neutrons, and other particles that interact with light, accounts for a surprisingly small percentage of the universe's total mass-energy. While models predict its abundance, roughly 30% remains unaccounted for – a discrepancy known as the "missing baryon problem."
The search for this elusive matter has led astronomers down unexpected paths. Recently, a unique tool has emerged: fast radio bursts (FRBs). These incredibly energetic pulses, originating from distant galaxies, offer a novel approach to mapping the universe's matter distribution. The key lies in the fact that as FRBs journey across vast cosmic distances, their passage through baryonic matter subtly slows them down – a phenomenon measurable by scientists on Earth.
The discovery of an FRB emanating from a seemingly "dead" galaxy, devoid of star formation, was particularly significant. This unexpected finding suggested that FRBs might be generated by processes far more prevalent than previously imagined, expanding their potential use in this quest.
Analyzing the dispersion measures – the amount an FRB's speed is altered by its passage through matter – allows astronomers to map the universe's baryonic matter. This technique is uniquely suited to this task because FRBs, with their high energy and long travel distances, readily interact with baryonic matter, unlike the enigmatic dark matter.
Initial studies using this method have already yielded remarkable results. By analyzing a collection of FRB dispersion measures, scientists have created preliminary models of the universe's structure. These models support existing cosmological models, estimating baryonic matter at approximately 5% of the total mass-energy, consistent with theoretical predictions.
More importantly, these studies provide compelling evidence for the location of the missing baryons. A significant portion, around 76%, appears to reside in the wispy, diffuse gas located between galaxies, forming a vast, interconnected cosmic web. This discovery resolves a longstanding puzzle and illuminates the distribution of matter in the universe.
The implications of this discovery extend far beyond the solution to the missing baryon problem. Understanding the distribution of baryonic matter is crucial for refining our models of galaxy formation, stellar evolution, and the behavior of supermassive black holes. The interplay between baryonic matter and these cosmic behemoths influences galactic growth and the overall evolution of the universe.
The field of FRB research is still in its infancy. While thousands of FRBs have been detected, only a few have had their origin pinpointed accurately. However, advanced radio telescope projects like CHIME and DSA-2000 are poised to dramatically increase the detection rate, potentially yielding thousands of well-localized FRBs annually. This abundance of data will allow astronomers to create much more detailed three-dimensional maps of the universe's baryonic matter, providing an unprecedented level of insight into the structure and evolution of the cosmos.
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Originally published at: https://www.livescience.com/space/astronomy/like-trying-to-see-fog-in-the-dark-how-strange-pulses-of-energy-are-helping-scientists-build-the-ultimate-map-of-the-universe
