Dark matter rules every galaxy. But what exactly is it? Astronomers believe it to be some kind of new, exotic particle. You may have heard some terms tossed around, like WIMPs or axions. Let’s explore what those terms actually mean.
First off, there’s a few things that we know about dark matter. Astronomers believe that dark matter is some kind of particle, previously unknown to physics. Whatever it is, it makes up about 80% of the mass of the universe. It barely interacts with light, if at all. It barely interacts with normal matter, if at all. It barely interacts with itself, if at all. We also know that it’s “cold”, which means that the individual particles don’t have very high velocities.
It basically just sits there and gravitates. But that gravity is essential: it keeps galaxies glued together and provides the scaffolding for the entire large-scale structure of the universe.
One of the earliest candidates for the dark matter particle are the WIMPs, for weakly-interacting massive particles. It’s not so much a name as a catch-all category. In this case, “weakly-interacting” means “interacts via the weak nuclear force” (although that interaction is also literally weak). WIMPs would be a ...