The explanation we name darkish matter darkish isn’t as a result of it’s some shadowy materials. It’s as a result of darkish matter doesn’t work together with gentle. The distinction is delicate, however necessary. Common matter could be darkish as a result of it absorbs gentle. It’s why, for instance, we will see the shadow of molecular clouds towards the scattered stars of the Milky Manner. That is attainable as a result of gentle and matter have a strategy to join. Gentle is an electromagnetic wave, and atoms include electrically charged electrons and protons, so matter can emit, take in and scatter gentle. Darkish matter isn’t electrically charged. It has no strategy to join with gentle, and so when gentle and darkish matter meet up they merely cross by way of one another.
All of our observations recommend that darkish matter and light-weight solely have gravity in frequent. When darkish matter is clustered round a galaxy, for instance, its gravitational tug can deflect gentle. Due to this we will map the distribution of darkish matter within the Universe by observing how gentle is gravitationally lensed round it. We additionally know that darkish and common matter work together gravitationally. The tug of darkish matter causes galaxies to assemble collectively into superclusters. However an unanswered query is whether or not darkish and common matter solely work together gravitationally. If an atom and darkish matter particle intersected, would they actually simply cross by way of one another?
Since we haven’t straight noticed darkish matter particles we will solely speculate, however most darkish matter fashions argue that gravity is the one frequent hyperlink with gentle and common matter. Darkish and common matter clump round one another, however they don’t collide and merge like interstellar clouds. However a brand new examine suggests the 2 do work together, which might reveal delicate facets of the mysterious stuff.
The examine seems at six ultrafaint dwarf galaxies, or UFDs. They’re satellite tv for pc galaxies close to the Milky Manner that appear to have far fewer stars than their mass would recommend. It is because they’re principally manufactured from darkish matter. If common and darkish matter solely work together gravitationally, then the distribution of stars in these small galaxies ought to observe a sure sample. If darkish and common matter work together straight, then this distribution shall be skewed.
To check this the workforce ran laptop simulations of each situations. They discovered that within the non-interacting mannequin the distribution of stars ought to grow to be extra dense within the middle of the UFDs and extra diffuse on the edges. Within the interacting mannequin the stellar distribution must be extra uniform. Once they in contrast these fashions with observations of the six galaxies, they discovered the interacting mannequin was a barely higher match.
So it appears darkish and common matter work together in methods past their gravitational tugs. There isn’t sufficient information to pin down the precise nature of the interplay, however the reality there may be any interplay in any respect is a shock. It signifies that our conventional fashions of darkish matter are a minimum of partly unsuitable. It could additionally level the best way towards new strategies of detecting darkish matter straight. In time we might lastly resolve the thriller of this darkish, however not totally invisible, materials.
Reference: Almeida, Jorge Sánchez, Ignacio Trujillo, and Angel R. Plastino. “The Stellar Distribution in Ultrafaint Dwarf Galaxies Suggests Deviations from the Collisionless Chilly Darkish Matter Paradigm.” The Astrophysical Journal Letters 973.1 (2024): L15.
