Half of the Matter in the Universe Is Missing. Astronomers May Have Found It Using Mystery Radio Signals From Deep Space

For decades, astronomers have known half of the matter in the universe is "missing." Through observations, researchers have been able to calculate how much matter existed just after the Big Bang. However the result posed a problem—there was a large discrepancy between how much matter there should be, and how much we could see.

It is thought this missing matter is located in intergalactic space—the voids between galaxies—and teams of scientists are using different techniques to pinpoint it. Last year, for example, researchers using NASA's Chandra X-ray observatory said they had tracked it down, suggesting it may be gathered in huge strands of gas in these voids.

In a study published in Nature, researchers led by Jean-Pierre Macquart, from Curtin University, Australia, have now used fast radio bursts (FRBs)—mystery signals from deep space—to find the missing matter. "We know from measurements of the Big Bang how much matter there was in the beginning of the Universe," Macquart said in a statement. "But when we looked out into the present universe, we couldn't find half of what should be there. It was a bit of an embarrassment. Intergalactic space is very sparse. The missing matter was equivalent to only one or two atoms in a room the size of an average office."

FRBs are extremely bright and short-lived radio signals that were first discovered in 2007. Because they are so short-lived, most of the first FRBs were only found in telescope data long after the event had passed, making tracing their source extremely difficult. While scientists do not know what could be producing these bursts, they appear to release huge amounts of energy—equivalent to what our sun produces in almost a century.

In recent years, with more dedicated efforts to understand the phenomenon, scientists have been able to trace several FRBs back to their source galaxy. Last month, one was even found coming from inside the Milky Way.

Macquart and colleagues were able to use these FRBs as "cosmic weigh stations." By measuring the distances of FRBs, they were able to work out the density of the universe. "The discovery of fast radio bursts and their localization to distant galaxies were the key breakthroughs needed to solve this mystery," study author J. Xavier Prochaska, from the University of California Santa Cruz, said in a statement.

Radiation from the bursts is spread out by the universe's missing matter "in the same way that you see the colors of sunlight being separated in a prism," Macquart said.

Calculations showed the amount of matter observed with the FRBs fit with observations from after the Big Bang. "The agreement between model and data is striking," the team wrote. "Effectively, the FRB measurements confirm the presence of baryons [the missing matter] with the density estimated from the cosmic microwave background and Big Bang nucleosynthesis, and these...measurements are consistent with all the missing baryons being present in the ionized [intergalactic medium]."

Stock image representing space. For decades, scientists have been searching for the universe's missing matter. iStock