Dark Matter — part 3

Introduction

In the past two posts, I’ve given you guys a bit of context for dark matter, however I haven’t covered exactly what dark matter is. So what is dark matter?

“The Universe is made mostly of dark matter and dark energy, and we don’t know what either of them is.”
- Saul Perlmutter

The quote pretty much sums things up. We have no idea what dark matter is. We do have a decent amount of data regarding it and we do believe that dark matter is one of the explanations for why stellar objects near the edge of the galaxy spins at that rate but we cannot say that dark matter exists with certainty

In fact, there are currently two main theories that try to explain the above phenomena:

1. MOND
2. Dark Matter

MOND stands for “Modified Newtonian Dynamics”. The theory basically states that the laws of classical mechanics work differently on a galactic scale. Dark Matter is the theory that there is basically this “substance” that adds mass to whatever it encompasses. This is a bit hard to imagine but that’s basically what Dark Matter is.

While MOND does have avid followers, dark matter is the more accepted theory as MOND does not provide a complete cosmological model. It has several shortcomings which will have a separate blogpost.

So now dark matter, what is it?

Well you can define it as a “substance” but it’s a bit more than that. We sometimes think of dark matter as a halo that can surround celestial objects. We believe that a dark matter halo encompasses the Milky Way which is what gives it additional mass.

An artist’s rendition of a dark matter halo

Now with that being said, there are two possible candidates for dark matter.

1. WIMPs
2. MACHOs

WIMPs stand for Weakly Interacting Massive Particles while MACHOs stand for Massive Compact Halo Object. WIMPs are subatomic particles (Like protons, neutrons and electrons) that are considered neutral in charge. They are hypothesised to make up all of dark matter. MACHOs are bodies independent of any celestial object that emits little to no radiation. This is also another proposed candidate for dark matter. If dark matter emitted radiation, we would detect high levels of radiation, we don’t.

But wait, there is another. We have the Axion, named after detergent powder, a suitable candidate for Dark Matter as well.

I’m going to end off here to prevent anymore confusion. In the next post, I’ll go more in detail about what WIMPs, MACHOs and Axions are. Hope you enjoyed!