11 September 2014
Darkish matter is a side of the universe we nonetheless don’t totally perceive. We now have a number of proof pointing to its existence (as I outlined in a sequence of posts some time again), and one of the best proof now we have factors towards a selected sort of matter generally known as chilly darkish matter (CDM). One huge draw back is that now we have but to search out any direct detection of darkish matter particles. In actual fact, most of the possible candidates for darkish matter have been all however eradicated. One other is that chilly darkish matter doesn’t agree with our observations of dwarf galaxies. Now a brand new paper presents an answer to the second drawback that may even assist with the primary.
The principle drawback with dwarf galaxies is that there are fewer of them round spiral galaxies than darkish matter predicts. Once we do darkish matter pc simulations, the outcomes all the time have extra dwarf galaxies than we observe. This has been taken to imply that both the simulations are one way or the other flawed, or darkish matter isn’t the entire resolution we’ve thought. This new work appears to be like at a modified model of darkish matter, and the way it results these sorts of pc simulations.
Usually, it’s assumed that darkish matter doesn’t work together with gentle instantly in any respect. This implies we will see its gravitational results, however we don’t see something reminiscent of absorption strains and the like, which we observe with common matter. The rationale for that is that darkish matter makes up nearly all of matter within the universe. About 90% of the mass in our personal Milky Approach consists of darkish matter. If it interacted a lot with gentle, then we might have seen its results on gentle by now. This new work proposes that darkish matter does work together with gentle, however solely very, very barely.
Now you may assume that if darkish matter interacts so barely with gentle that we don’t see its impact, then it definitely can’t differ that a lot from commonplace darkish matter, however the group confirmed that this very small impact can construct up over time, in order that trendy galaxies have fewer dwarf satellites, simply as we observe. You’ll be able to see this within the picture above. The highest left picture is commonplace darkish matter mannequin, with too many satellite tv for pc dwarf galaxies. The highest proper is a heat darkish matter mannequin that solves the dwarf galaxy drawback however doesn’t agree with different observations. The underside left is that this new, gentle interacting darkish matter mannequin, and the underside proper is what occurs if you make the sunshine interplay too sturdy and get no dwarf galaxies.
So by modifying darkish matter to incorporate slight interactions with gentle, the predictions match dwarf galaxy observations. It needs to be famous that simply because this modification works, that doesn’t imply it’s the resolution. Tweak theories are weak theories, as I’ve mentioned earlier than. This sort of darkish matter may additionally have an effect on different issues reminiscent of massive scale construction, and this might should be studied earlier than we may very well be assured about this explicit mannequin. However the work does present that darkish matter fashions can tackle a number of the recognized issues with darkish matter.