After almost 20 years of research and thanks to the help of the XMM-Newton X-ray space observatory, a team of scientists from the University of Boulder in Colorado (USA) has found evidence of that small percentage in the burning intergalactic gas of ordinary matter so difficult to trace: the last reservoir of ordinary matter hidden in the universe.
Equation of the universe: baryonic matter + dark matter + dark energy
Ordinary matter represents approximately 5% of the total mass of the universe (planets, stars, galaxies ... and a large amount of newly discovered visible matter). The rest of the universe is 25% dark matter and 70% dark energy.
Ordinary matter, or "baryons", therefore, constitutes all existing physical objects, from the stars to the nuclei of black holes. But until now, astrophysicists have only been able to locate approximately two thirds of the matter that theoreticians predict was created by the Big Bang.
"The lost baryons are one of the greatest mysteries of modern astrophysics, we know that this matter must be out there, we see it in the early universe, but then we lose sight of it." Where does it go? "Explains Fabrizio Nicastro, Italian Institute of Astrophysics and leader of the study collected by the journal Nature.
In the new research, the international team of scientists found it in the space between the galaxies. Observing in the ubiquitous filaments of the cosmic network in the electromagnetic spectrum, they were able to detect really hot intergalactic gas, with temperatures of around one million degrees (or more), which was blocking the X-rays emitted by even more distant sources, as exposed Michael Shull, co-author of the work.
The finding is an important step for astrophysics. "This is one of the key pillars to prove the Big Bang theory: calculate the baryon census of hydrogen and helium and everything else in the periodic table," says Shull.
Searching in the Hot Intergalactic Medium (WHIM)
To find the missing atoms to discover, astrophysicists pointed a series of satellites to a quasar called 1ES 1553, a black hole in the center of a galaxy that is consuming and spitting huge amounts of gas. "It's basically a really bright beacon in space," said Shull.
Scientists can obtain much information by recording how radiation from a quasar passes through space, such as when a sailor sees a lighthouse through fog. First, the researchers used the Cosmic Origins Spectrograph on the Hubble Space Telescope to get an idea of where they might find the lost baryons. Next, they focused on the baryons used by the X-Ray Multi-Mirror Mission (XMM-Newton) of the European Space Agency. Finally they found the signature of a type of highly ionized oxygen that lies between the quasar and our solar system, and at a density high enough to, when extrapolated to the entire universe, represent that last percentage that was missing from ordinary matter.
"We found the missing baryons," Shull said. The scientist suspects that galaxies and quasars hurled that gas into deep space for billions of years.
It is the beginning of a new search, since we will have to confirm these findings by pointing satellites to even brighter quasars.
"The discovery with XMM-Newton of the missing baryons is an exciting first step to fully characterize the circumstances and structures in which these particles are found," says Jelle Kaastra of the Dutch Institute of Space Research and co-author of the study.
The intergalactic gas constitutes most of the ordinary matter of the cosmos which, in turn, only represents 5% of the total universe.