Dark Matter 101

What is Dark Matter?

Well you can’t just jump straight into it! You need background.

Ok, give me the background.

In the 1930s, astrophysicists named Jan Oort and Fritz Zwicky were observing stars in the Milky Way galaxy, and they came to the realization that stars in galaxies don’t follow the normal rotational velocities that are expected. As the distance from the center of the galaxy increases, stars are supposed to slow in their orbits, but what is actually observed is the stars orbit at a constant velocity. The expected velocities are shown in the chart labeled as “disk”, and the uppermost line is the measured data.

Screen Shot 2015-07-11 at 1.04.33 AM

Why?

Well, Oort and Zwicky thought there had to be something else in the galaxies that caused them to spin this way, and the only explanation was something that we couldn’t see, something that doesn’t interact with light, hence the name Dark Matter

Mind. Blown.

It gets better. Everything we see, stars, black holes, you, me, etc. only makes up about 5% of the universe. 27% is Dark Matter, which only (as far as we know) interacts gravitationally on a cosmic scale, the rest is Dark Energy, and we have absolutely no idea what that is.

What does that mean for the universe?

Well, we know that without Dark Matter, the early universe wouldn’t have “clumped” into galaxies and stars and planets and basically everything else. So Dark Matter is kind of important.

Now What?

Until now, we have only had evidence of Dark Matter, but no concrete proof that it exists. There are a lot of candidates for what we think a DM particle might look like, but we have no definite proof. The best candidate we have theorized is called a WIMP, which means “Weakly Interacting Massive Particle”.

What does that even mean?

Well we know the 4 forces, one of which is the Weak Nuclear Force. That is how we assume that a DM candidate would interact with another particle.

Okay, I think I’m getting it…

We have a problem though. Every signal has a background, and unfortunately, the background rates for Dark Matter ridiculously overpower any Dark Matter event interaction we are looking for.

Well that is a problem…

The only ways to fix that are to have extremely clean materials (radioactively pure), and good discrimination programs to be able to tell background events apart from the actual event.

That’s where I come in 😉

I’m doing research at SMU specifically to help reduce backgrounds for Direct DM experiments. More on that to come later!

//Moez

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