Astronomers have long been puzzled by a missing piece of the universe. While we are familiar with the ordinary matter that makes up everything we see—planets, stars, and galaxies—there’s always been a significant gap in our understanding. Nearly 40% of the universe’s regular matter was unaccounted for until now.
A new study confirms that simulations of this missing matter were correct, and the material was hiding in plain sight between galaxies, spread out in an enormous, invisible web.
Fast Radio Bursts Reveal Hidden Matter
The breakthrough came from studying Fast Radio Bursts (FRBs), powerful flashes of radio waves that last mere milliseconds. These mysterious signals are known to interact with matter in space, causing a phenomenon known as “dispersion,” which spreads out the frequency of the signal. By carefully analyzing how the signals changed as they traveled through space, scientists could estimate how much matter exists between galaxies.
The study published in Nature, which involved 69 FRBs from known sources, measured how the signal from these bursts slowed down due to this interaction with the gas in the intergalactic medium. Liam Connor, assistant professor at Harvard and lead author of the study, explained: “The FRBs shine through the fog of the intergalactic medium, and by precisely measuring how the light slows down, we can weigh that fog, even when it’s too faint to see.”
This research finally gave astronomers the tools to quantify the previously invisible matter in the space between galaxies, confirming earlier predictions made by theoretical models.
Credit: ESA/XMM-Newton and ISAS/JAXA
X-Ray Observations Confirm the Findings
The discovery was confirmed by X-ray observations of the intergalactic gas. Although faint, this gas emits X-rays due to its high temperatures, reaching millions of degrees. Detecting these emissions is incredibly difficult, which is why two space telescopes—Europe’s XMM-Newton and Japan’s Suzaku—were used to gather the necessary data. Together, they focused on the Shapley Supercluster, one of the largest structures in the universe, containing more than 8,000 galaxies.
By studying X-rays from this supercluster and its surrounding gas, astronomers were able to measure the gas in the vast filaments that connect galaxies in the cosmic web. These filaments span enormous distances, including one stretching 23 million light-years. The data gathered from both the radio and X-ray observations closely aligned with predictions from current cosmological models.
Credit: ESA
A New View of the Cosmic Web
The discovery of the missing matter doesn’t just fill in a gap in our understanding of the universe’s composition. It also deepens our knowledge of how galaxies and clusters are arranged within the cosmic web. This vast network of galaxies, gas, and other structures shapes the universe, and understanding the distribution of matter within it is essential for further study.
Konstantinos Migkas, lead researcher from Leiden Observatory, commented on the significance of the findings: “For the first time, our results closely match what we see in our leading model of the cosmos – something that’s not happened before.” This validation of existing models marks a major milestone in the field of cosmology.