Dark matter is one slippery substance. It must, as long as we can tell, be capable of working on our present Universe models. But not only can we not see it, feel it, or interact with it in any way we''re not sure what dark matter is.
We have a few clues, such as how dark matter may ''talk'' to regular matter via gravity. A new paper argues that something called''non-minimal coupling'' might be the solution.
"We asked ourselves: Is gravity wrong or is we just missing something crucial about dark matter''s nature? What if dark matter and standard ''baryonic'' matter do not communicate in the manner we have always imagined," Giovanni Gandolfi, Andrea Lapi, and Stefano Liberati, together, discuss their findings in a press release.
"With our research, we have attempted to answer these difficult questions."
Our finest guess about what dark matter might be is cold, weakly interacted massive particles, which experimental physicists around the world have tried to detect for decades, but haven''t yet been identified.
Despite the effectiveness of this particular type of dark matter in our models, there are still a number of issues. One is the cuspy halo problem, where the inferred density of dark matter in galaxies does not match up with what''s known as N-body simulations.
In low-matter galaxies dark matter, these simulations suggest that a ''cuspy'' approach should be used to explain their current structure and movement, meaning it is most concentrated around the cusp or outside of the galaxy. However, these observations suggest that most dwarf galaxies seem to keep their dark matter in the middle.
This paper is certainly not the first and will likely not be the last to investigate and resolve these dark matter issues, but the team has suggested a new approach. According to researchers, dark matter is non-minimally linked to gravity, thus it resolves the cuspy issue and another related problem, called radial acceleration ratio.
"In this paper, we propose a second approach to modify the standard cold dark matter framework, which is capable of accurately describing the observed galaxy rotation curves, while also to faithfully reproduce the radial acceleration relationship," the team says.
"Incorporating such a coupling can prolong the successfulness of the cold dark matter on large cosmological scales while improving its behavior in galactic systems."
Non-minimal coupling is a mistake. It means that the dark matter is directly coupled to a curvature in spacetime, called theEinstein tensor. Simply put, it is a new type of interaction between dark matter and gravity. If non-minimal coupling is occurring, the dark matter interforms with spacetime in a different manner than regular matter.
"This feature of dark matter isn''t a part of any new exotic fundamental physics," the authors say.
"One can explain the existence of this non-minimal coupling with known physics alone."
This is simply one assumption, and although it isn''t quite compatible with the observational data we have so far, dark matter is still a complicated beast. We''ll need more research to prove if non-minimal coupling is a feature of dark matter, or another assumption that pushes us forward to discover what''s happening.
In a press statement, the authors reveal that "The future of dark matter" appears to be brighter.
"We will conduct further research to investigate all the beneficial implications of this proposed new feature of dark matter. We wouldn''t be surprised to discover that this non-minimal coupling might answer other unknown questions of the Universe."
The Astrophysical Journal has published these findings.