What is dark matter? No one knows. But it's there, apparently, making up the vast majority of the mass of the universe. Or at least, that's what the math says. Now some scientists think that the math might be wrong, and there might be another explanation for the apparent density of the universe. In some ways that's a more likely scenario. After all, every one of science's attempts to detect and conclusively prove the existence of dark matter has failed. Despite this lack of conclusive proof, the vast majority of physicists believe that dark matter is real and it does make up the majority of the universe. It's just finding it that's the problem.
Well, like a lot of impossible-to-find things, dark matter may have already been found. According to a paper recently published in the Journal of Physics G by physicists Mikhail Bashkanov and Daniel Watts, dark matter may be made of a subatomic particle called a d*(2380) hexaquark, or "d-star," a six-sided quark which was probably discovered by German scientists in 2014. Quarks and gluons are the bizarre subatomic particles that form protons and neutrons.
Most other explanations for dark matter revolve around new and never-before-observed particles that lie outside the Standard Model of physics. But Bashkanov and Watts believe that dark matter might be made of these "d-star" quarks. On their own, the d-star quarks couldn't explain dark matter. They would decay much too quickly. But Bashkanov and Watts believe that during a brief period of time at the beginning of the universe, these quarks could have formed together in a type of matter called a Bose-Einstein Condensate (BEC).
If this were true, it would explain why we can't find dark matter. It would be impossible for us to interact with. The Bose-Einstein Condensate would have mass, but no electromagnetic charge. The force that keeps objects separate and allows interaction between them (like my fingers pressing the keys on my keyboard without going right through my computer) is the electromagnetic force holding the atoms together. A d-star BEC, the physicists write, could theoretically be perfectly neutral with no electromagnetic charge. Without that, dark matter would pass through other matter like a ghost without ever interacting with it. It would, however, exert a gravitational pull on the outside universe.
There was only a brief period in our universe's life when this type of dark matter could have been made. In the time immediately after the Big Bang, the universe was a soup of quark-gluon plasma that hadn't yet solidified into the particles that make up the known universe. Eventually, the universe cooled and the quark-gluon soup solidified into more stable particles. Bashkanov and Watts say this transitional period had all the right conditions for some of the d-star hexaquarks to form the hypothetical Bose-Einstein Condensate that we now call dark matter.
If this is the explanation for dark matter, the scientists say that we may be able to detect it. While BECs are extremely long-lived, they do sometimes decay around Earth. Bashkanov and Watts say that the decay of the dark matter BECs would have a particular signature that would look as if it was coming from every direction at once. Now, they say, the next step is to look for that signature.
Has the mystery been solved? Who knows. It's worth pointing out again that literally every other time someone has said they knew how to detect dark matter, they've been completely wrong.