Although abundant, it cannot be seen, collected, analyzed, but it is there – the gravitational effect that dark matter has is so great that it was possible to estimate that it constitutes 80% of the mass of the Universe. Investigating how it came about can give clues as to what it is and what its role in cosmic balance is.
“Is dark matter a collection of elementary particles? If so, what are the properties of these particles? What forces do they exert and what interactions do they experience? When was dark matter created and what structures played an important role in its formation?” said astrophysicist Andrew Long of Rice University, co-author of the study now published in The Physical Review Letters.
The consensus is that it came after the Big Bang, the event that gave rise to our Universe; but how did it form? This is what Long and more physicists Michael Baker, from the University of Melbourne, and Joachim Kopp, from Johannes Gutenberg University in Mainz, focused on.
Time and the Universe had not yet counted a nanosecond and particles were created, clashing and annihilating each other – the chaos before the cosmos, which at that time was an incredibly hot and dense primordial soup of extremely energy elementary particles high.
When the Universe started to expand and the plasma started to cool, the production of new particles stopped. The ones that existed stopped crashing, and the ones that survived the hellish beginning of the cosmos are the so-called “thermal relics” – protons, neutrons and everything else that constitutes matter.
The hypothesis that Long and the other physicists imagined is: what if dark matter were made up of particles – themselves, “thermal relics”?
They would have been born from the hot plasma which, almost immediately after the Big Bang, changed state as water or iron change – from one state to another, solidifying by evaporating or liquefying. What the three scientists imagined was that bubbles of cooled plasma abruptly formed in the extremely hot primordial broth in the early universe, expanded and eventually merged, in a continuous process until the entire universe started to cool and expand .
“As these bubbles expand throughout the universe, they act as filters that separate the particles of dark matter from the plasma. Thus, the amount of dark matter that we measure in the universe today is a direct result of this filtration in the first fractions of second after the Big Bang, “said Long.