Scientists may have found an answer to the mystery of dark matter. It involves an unexpected byproduct
All the matter we can see — stars, planets, cosmic dust and everything in between — can’t account for why the universe behaves as it does, and there must be five times as much of it around for researchers’ observations to make sense, according to NASA. Scientists call that dark matter, because it does not interact with light and is invisible.
In the 1970s, astronomers confirmed dark matter’s existence by looking at stars orbiting at the edge of spiral galaxies. They noted that these stars were moving too fast to be held together by the galaxy’s visible matter and its gravity — they should have been flying apart instead. The only explanation was a large quantity of unseen matter, binding the galaxy together.
Since then, scientists have been trying to observe dark matter directly and even built large devices to detect it — but so far, with no luck.
Early in the search, a physicist postulated that dark matter could be hiding in black holes — the main subject of his work — formed during the big bang.
Now, a new study has brought the theory back into the spotlight, revealing what these primordial black holes were made of and potentially discovering an entirely new type of exotic black hole in the process.
The study reveals that these black holes must have appeared in the first quintillionth of a second of the big bang. In our everyday world, we cannot find protons and neutrons broken apart, she added, and they act as elementary particles. However, we know they are not, because they are made up of even smaller particles called quarks, joined together by other particles called gluons.
Such a formation would make them fundamentally different from the astrophysical black holes that scientists normally observe in the universe, which are the result of collapsing stars. Also, a primordial black hole would be much smaller — only the mass of an asteroid, on average, condensed into the volume of a single atom. But if a sufficient number of these primordial black holes did not evaporate in the early big bang and survived to this day, they could account for all or most dark matter.
During the making of the primordial black holes, another type of previously unseen black hole must have formed as a kind of byproduct, according to the study. These would have been even smaller — just the mass of a rhino, condensed into less than the volume of a single proton.
These minuscule black holes, due to their small size, would have been able to pick up a rare and exotic property from the quark-gluon soup in which they formed, called a ‘color charge.’ It is a state of charge that is exclusive to quarks and gluons, never found in ordinary objects. This color charge would make them unique among black holes, which usually have no charge of any kind.
However, if they were still around just ten millionths of a second into the big bang, when protons and neutrons formed, they could have left observable signatures by altering the balance between the two particle types.
The measurement could come from Earth-based telescopes or sensitive instruments on orbiting satellites. But there could be another way of confirming the existence of these exotic black holes.
‘Making a population of black holes is a very violent process that would send enormous ripples in the surrounding space-time. Those would get attenuated over cosmic history, but not to zero. The next generation of gravitational detectors could catch a glimpse of the small-mass black holes — an exotic state of matter that was an unexpected byproduct of the more mundane black holes that could explain dark matter today.’
There’s also the possibility that primordial black holes are just a fraction of the dark matter. ‘It doesn’t really have to be all the same. There are five times more dark matter than regular matter, and regular matter is formed from a whole host of different particles. So why should dark matter be a single type of object?’
The study is exciting and proposes a novel mechanism of formation for the first generation of black holes. ‘All the hydrogen and helium that we have in our universe today was created in the first three minutes, and if enough of these primordial black holes were around until then, they would have impacted that process and those effects may be detectable.’