Astrophysicists have made a groundbreaking discovery by tracing powerful radio signals back to their host galaxies, revealing the location of the Universe's elusive missing matter. These findings shed light on the vast space between galaxies, where matter exists in such a tenuous state that it has remained undetectable by the naked eye. The research demonstrates that sufficient quantities of this matter drift in the cosmic void, becoming detectable through fast radio bursts (FRBs)—phenomena that possess the energy equivalent of about 500 million Suns.
The long-standing mystery known as the missing baryon problem has puzzled scientists for decades. According to Liam Connor, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, the issue was never about the existence of this matter; it was always about its location. Recent advancements in using FRBs have led to a significant discovery: approximately three-quarters of the missing baryonic matter is residing in the cosmic web, the expansive structure that connects galaxies.
Baryonic matter, which constitutes about 5 percent of the total matter-energy composition of the Universe, includes everything we can observe—stars, galaxies, planets, dust, black holes, gas, and even humans. The Cosmic Microwave Background, a remnant glow from the Big Bang, provides crucial data about the amount of baryonic matter present at the Universe's inception. However, a comparison of this initial amount with the visible matter detected in the sky reveals a substantial discrepancy—only about half of the expected baryonic matter is visible.
In recent years, astronomers have begun to uncover clues about this missing matter, particularly in the vast and nearly-empty space that exists between galaxies. Although traditional instruments have struggled to detect this elusive matter, researchers have identified that the presence of baryonic matter is sufficient to stretch the millisecond signals emitted by FRBs. These bursts, characterized by their rapid and explosive nature, are a cosmic enigma. Current theories suggest that they may originate from erupting magnetars, with signals traveling from various distances across the Universe, some spanning an astounding 9.1 billion years.
Connor and his team meticulously analyzed 60 FRBs, focusing on each signal to identify the characteristics indicating their passage through baryonic matter on their journey to Earth. “FRBs act as cosmic flashlights,” Connor explains. “They shine through the fog of the intergalactic medium, allowing us to weigh that fog even when it’s too faint to observe directly.”
The findings from this research indicate that a significant portion of the normal matter in the Universe—approximately 76 percent—is located in the voids of the intergalactic medium, primarily as hydrogen gas. An additional 15 percent is found within the dark matter halos that encircle galaxies and clusters, while the remaining matter comprises the galaxies themselves, including stars and the interstellar medium.
As astronomers continue their quest to locate baryonic matter throughout the Universe, understanding its distribution and origins will offer valuable insights into the evolution of the Universe over its 13.8 billion-year history. This recent breakthrough not only answers the question of where the missing matter is located, but it also raises new inquiries about how it came to be there. Vikram Ravi, an astronomer at Caltech, describes the findings as “a triumph of modern astronomy.” He highlights that we are beginning to perceive the Universe's structure and composition in an entirely new light, thanks to the revelations provided by FRBs. These fleeting flashes enable us to trace the otherwise invisible matter that fills the immense spaces between galaxies.
