Long-standing Mystery of Universe's Hidden Matter Finally Solved

Where is the universe's missing matter? iStock

An international team of researchers has located the last of the universe's missing ordinary matter—a finding that finally answers a long-standing mystery in the field of astrophysics and shines new light on our understanding of the cosmos.

This matter, known as baryons, makes up all physical objects in existence. But scientists have only been able to identify around two-thirds of the baryons that should have been created by the Big Bang—a dilemma referred to as the "missing baryon problem."

It is thought that around 60% of baryons exist in the diffuse clouds of gas that fill the vast space between galaxies, while another 10% can be found inside the galaxies themselves. It is important to note that baryons are distinct from the theoretical dark matter that is predicted to make up the majority of the universe's mass.

To locate the missing 30%, the research team—which was led by the Italian Istituto Nazionale di Astrofisica (INAF) and the Harvard-Smithsonian Center for Astrophysics—analyzed radiation emitted by a distant object called 1ES 1553.

1ES 1553 is a quasar—an extremely bright object found in the center of some distant galaxies that are powered by gas spiraling at high velocity into supermassive black holes. Quasars are some of the brightest objects in the universe and can outshine all of the stars in their host galaxies, making them visible even from distances of billions of light years.

"It's basically a really bright lighthouse out in space," Michael Shull, an astrophysicist from the University of Colorado Boulder and co-author of the study, said in a statement.

By analyzing how radiation from the quasar passes through space, the scientists found signatures of a form of oxygen gas in web-like patterns, known as the warm-hot intergalactic medium (WHIM), located in regions that lie between 1ES 1553 and our Solar System.

"This is where nature has become very perverse," Shull said. "This intergalactic medium contains filaments of gas at temperatures from a few thousand degrees to a few million degrees."

When the researchers extrapolated the density of the gas in this region to the entire universe, they found it could account for the hidden 30% of matter. The findings are published in the journal Nature.

"We found the missing baryons," Shull said.

The results are significant because they resolve the long-standing mystery and provide new insights into fundamental questions of how the universe began, he added.

"This is one of the key pillars of testing the Big Bang theory: figuring out the baryon census of hydrogen and helium and everything else in the periodic table," he said.

However, the researchers still need to confirm their findings by analyzing the radiation from different quasars.