Does dark matter interact with the kind of matter we're made of? Astrophysicists have long puzzled over the relationship between dark matter and the visible (or baryonic) matter that comprises stars, galaxies, and everything else we can directly observe. In a study recently published in the journal The Astrophysical Journal, researchers explain how the two types of matter interact.
The authors of the study suggest that dark matter communicates with visible matter through a unique method called “non-minimal coupling with gravity.” This method allows the dark matter to directly couple with Einstein Tensor, a curvature in spacetime that follows the laws of conservation of energy and momentum. Einstein tensor is mentioned in Einstein's field equations originally published in the year 1915.
If the researchers are right, then it makes sense that dark matter wouldn't interact with spacetime the way baryonic matter does.
Dark matter and visible matter talk differently
The authors of the study — Giovanni Gandolfi, Andrea Lapi, and Stefano Liberati — analyzed data from numerous spiral galaxies. Based on their study, they propose that maybe dark matter and baryonic matter interact in a way that is not expected by us. For instance, generally, it is assumed that there is no difference in the way both forms of matter perceive spacetime. However, if non-minimal coupling exists then this suggests otherwise.
The researchers note, "We asked ourselves - is gravity wrong or are we just missing something crucial about dark matter's nature? What if dark matter and standard 'baryonic' matter do not communicate in the way we have always imagined?"
Many physicists believe that dark matter is mostly made up of hypothetical weakly interacting massive particles. However, until now, scientists are unsure of the existence of such particles because nobody has ever detected the same. On the other hand, some cosmologists in the past have shed light on the relation between gravity and dark matter and even proposed that the latter has originated from gravitons (hypothetical quantum units that collectively give rise to gravitational force).
The recent study also highlights the crucial role played by gravity in the interaction between visible and dark matter. It mentions that non-minimal coupling leads to a change in the gravitational influence exerted by dark matter on regular matter, and this is probably how the two different forms of matter interact with each other.
Another answer to the non-believers
Dark matter is considered one of the most debatable topics within the scientific community. From time to time, research papers and reports are published from both sides that favor and argue the existence of dark matter.
Scientists who question the presence of dark matter generally point out that if a matter has never been detected, never revealed itself in the presence of any type of electromagnetic radiation, and never even found to have interacted with the visible matter then most probably, it doesn't exist. However, according to Gandolfi and his team, “dark matter is everywhere and it is an integral part of our universe interconnecting galaxies and various other elements.
They said, “among other things, the positions of those who argue that dark matter does not exist, and therefore gravity must be modified, are based on the difficulty of finding an explanation to this problem, which is one of the last missing pieces for a global comprehension of dark matter”. While talking about the possibility of non-minimal coupling, the authors further added, “This feature of dark matter is not a piece of new exotic fundamental physics. One can explain the existence of this nonminimal coupling with known physics alone.”
Gandolfi also highlights that their study is just one hypothesis so more research work is required to further examine and confirm the special property of dark matter discussed in their paper.