By tracking powerful radio signals back to their host galaxies near the beginning of time, astrophysicists have identified the whereabouts of the Universe's missing matter.

In the vast expanse between galaxies, a barely visible matter exists in quantities detectable through fast radio bursts (FRBs), which possess the energy of 500 million Suns.

This discovery contributes to solving the long-standing mystery of the missing baryonic matter in the Universe, a puzzle that has baffled scientists for years.

Astrophysicist Liam Connor from the Harvard-Smithsonian Center for Astrophysics explains, 'The missing baryon problem was never about the existence of matter but rather its location. Now, FRBs have revealed that three-quarters of it resides between galaxies in the cosmic web.'

Normal matter, composed of baryonic particles, constitutes about 5 percent of the Universe's matter-energy content. It encompasses everything that can be directly observed, such as stars, planets, galaxies, and even humans.

Thanks to the Cosmic Microwave Background radiation, a remnant of the Big Bang, scientists have an estimate of the initial baryonic matter present. Discrepancies arose when this amount was compared to the visible matter in the Universe, revealing a significant deficit.

In recent years, researchers have started to uncover hints of the missing matter in the sparse regions between galaxies. Although this matter is too faint to be detected by conventional instruments, it was found to affect the signals of FRBs.

FRBs are rapid and explosive bursts of radio waves that last for a fraction of a second. While their exact origin remains a mystery, they are believed to originate from erupting magnetars.

By studying 60 FRBs, Connor and his team analyzed the signals to identify traces of baryonic matter. These signals act as 'cosmic flashlights,' penetrating the intergalactic medium and allowing researchers to measure the density of this matter.

According to the study, the majority of normal matter in the Universe exists in the intergalactic medium, primarily as hydrogen gas (76 percent). Another 15 percent is located in dark matter haloes surrounding galaxies, with the remaining portion comprising stars and interstellar medium within galaxies.

Astronomers will continue to explore the distribution and origins of baryonic matter, shedding light on the evolution of the Universe over billions of years. While the location of the missing matter has been identified, the mechanisms behind its placement remain a subject of further investigation.

'This marks a significant advancement in astronomy,' says astronomer Vikram Ravi from Caltech. 'FRBs offer a unique perspective on the Universe's structure and composition, allowing us to uncover the invisible matter that occupies the vast spaces between galaxies.'

The findings have been published in Nature Astronomy.