Isn't this article related to dark energy and not dark matter...? Plus, it's not really a picture of dark matter, either...it's just some gravitational lensing with a false-colour overlay.
I'm no physicist, but as far as I understand it.. dark energy is the theoretical cause for the universe's expansion. Dark matter is the collection of gravity that cannot be particularly explained. The idea is: astronomers and scientists found ways of calculating the way gravity affects the movement of stars, planets, etc. and when there is a difference between the calculation and observed changes, dark matter/energy is said to be the cause until we figure out exactly what it is and what it's doing. The image shown is an area that is particularly dense with dark matter. Meaning there is a lot of unexplained gravity. It's concentrated so much that it is somehow creating a dark purple hue when viewed from afar. I think you're referring to anti-matter. Anti-matter is the physical opposite of matter. Like positive versus negative charges, only with regards to all matter. When particles of matter and anti-matter collide, they "cancel each other out" and turn into pure energy, which causes an explosion. If someone else is more familiar with any of this, I would appreciate any corrections.
