After almost 20 years of searching 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 fiery intergalactic gas. of ordinary matter so difficult to trace: the last reservoir of ordinary matter that hides in the universe.
Equation of the universe: baryonic matter + dark matter + dark energy
Ordinary matter represents about 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 stars to the cores of black holes. But until now, astrophysicists had only been able to locate about two-thirds of the matter that theorists 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 did it go?” Italian Institute of Astrophysics and leader of the study included in the journal Nature .
In the new research, the international team of scientists found it in the space between galaxies. Noting in the ubiquitous filaments cosmic web in the electromagnetic spectrum could be detected intergalactic gas actually hot, with temperatures of around a million degrees (or more), which was blocking X – rays emitted by even more distant sources, as described Michael Shull, co-author of the work.
The finding is an important step for astrophysics. “This is one of the key pillars for testing the Big Bang theory: calculating the baryon census of hydrogen and helium and everything else on the periodic table,” says Shull.
Searching the Hot Intergalactic Medium (WHIM)
To search for the atoms that were yet to be discovered, astrophysicists pointed a series of satellites at a quasar called 1ES 1553 , a black hole at the center of a galaxy that is consuming and spitting up enormous amounts of gas. “It’s basically a really bright beacon in space,” Shull said.
Scientists can get a lot of 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 missing baryons. They then focused on the baryons used by the European Space Agency’s X-Ray Multi-Mirror Mission (XMM-Newton) satellite. They finally found the signature of a highly ionized type of oxygen found between the quasar and our solar system, and at a density high enough that, when extrapolated to the entire universe, it represents that last missing percentage of ordinary matter.
“ We found the missing baryons ,” Shull commented. The scientist suspects that galaxies and quasars spewed this gas into deep space over billions of years.
It is the beginning of a new search, as these findings will have to be confirmed by pointing the satellites at even brighter quasars.
“The XMM-Newton discovery of the missing baryons is an exciting first step in fully characterizing the circumstances and structures in which these particles are found,” says Jelle Kaastra of the Netherlands Institute for Space Research and co-author of the study.
Reference: F. Nicastro et al, Observations of the missing baryons in the warm – hot intergalactic medium, Nature (2018). DOI: 10.1038 / s41586-018-0204-1
Image credit: NASA, ESA, E. Hallman (CU Boulder)
Intergalactic gas makes up most of the ordinary matter in the cosmos, which, in turn, only represents 5% of the total universe.
