Science Spotlight: Dark Matter & Energy

We are going to start our first “Science Spotlight” with the most luminous thing of all, dark matter and dark energy. What the heck is that? How’ve I never heard of that before? Should I be scared? If you’re thinking any of those things, then don’t worry, this is the place for you!

But first of all…

What is Dark matter?

First let's talk about normal matter for a second. This literally takes up anything that we can directly observe (you can say that it … matters).This means that its visible through our own eyes or through a telescope that picks up on light that we can’t see.There are three main states of matter, gas, water and solid (A additional state of matter in space is plasma. Additionally, scientists are trying to reach and detect new states of matter such as the Bose - Einstein condensate which is when subatomic particles are cooled down to 0 Kelvin - a universal unit for temperature).

Dark matter, like our normal matter, takes up space and holds mass. However, unlike matter, dark matter doesn’t absorb, reflect or radiate light (at least not a degree that is detectable).  Scientists predict that dark matter takes up 27% of the cosmos- but they still don’t quite don’t know what it is.

How do we know that dark matter exists?

So, if we can’t detect dark matter using our technology, nor do we know what it is made of, how are we so sure that it exists?

Short answer: It’s the only reasonable explanation.

Here’s the long answer. We know dark matter exists from its effects on other stars and galaxies. It’s the same idea as when you know someone is pushing you and your friends away from a line, but you can’t find out who. 

But, while dark matter doesn’t react to light (or does so very weakly), it does interact with another fundamental force, gravity. Through this gravity, scientists have been able to figure out and even map where dark matter is located. This altered gravity was first observed in 1933 by astronomer Fritz Zwicky. While observing the Coma Cluster  of galaxies, Zwicky observed that galaxies in the clusters were moving way too fast when compared to the gravity of the visible mass in the cluster. 

Because of this, Zwicky hypothesized that there was a new hidden type of matter that was causing the speed up of galaxies, leading to the first instance of dark matter. While now he is known for this theory (and is called the Father of Dark matter), his idea didn’t gain much popularity until after his death.

The next scientist who hypothesized about the existence of invisible matter was Carnegie astronomer Vera Rubin. Her observations helped to confirm Zwicky’s theory, especially on her work with spiral galaxies. She noticed that stars on the edge of these galaxies moved at the same speeds as the stars in the dense centers.

This also meant that the amount of this invisible mass was huge. There was a significant difference between the predicted and observed speed that could only be accounted for by a substantial amount of mass, in fact, Rubi calculated that the matter that we can see is only just 10% of their mass.

Since then, astronomers have been using Rubin’s work on the gravitational influence on dark matter to predict and locate possible areas of dark matter. 

But, before we dive in deeper about the mapping of dark matter, let's take a step back and learn about one important theory: The theory of General Relativity.

Theory of General Relativity: 

I know I know, this sounds super fancy, and it sounds hard to understand. Trust me, I’ll break it down nice and slowly so that you can understand. (And if you still can’t understand, then… I don’t know what to say). 

This theory, created by Albert Einstein, deals with something called space-time. Yeah, it sounds kinda stupid, but it's a key topic that we should know about before we talk anymore about this theory. 

Space-time or sometimes called the fabric of space time is a conceptual model that combines the 3 dimensions of space (what we are used to, x,y and z) and the dimension of time. In short, this means that space is measured in 4 dimensions instead of 3. Space time is visualized as a fabric or a grid, and like fabric, when something heavy (like a mass of big star) is placed on it, the fabric bends around. And if you place smaller objects on the fabric, they naturally go towards that big object, which explains why smaller stars orbit around larger ones.

But, what’s the point of this? Well, this actually makes it easier for scientists to think about they dynamic behavior of the different objects in space and how they affect each other!

Where is the Dark Matter?

So, using Albtert Einstein's theory of relativity, scientists figured out that dark matter exists in web-like structures on the fabric of spacetime, and we can visually see its effects. But how did they figure this out if the actual dark matter is invisible? Astronomers did this by seeing its effects of gravitational lensing (a phenomenon that occurs when a large object's gravity bends the path of light, similar to how a lens can bend light). NASA observed 135 of these images and 42 background galaxies to calculate the position of dark matter.

A more recent discovery led by the Atacama Cosmology Telescope collaboration reveals the most detailed map of dark matter that we have seen.

They did this by making a mass map using distortions from the Big Bang (Want to know what that is? Comment down below and I’ll make a separate blog for that!) This technique shows lumps of dark matter, most agree that this is because of the uneven distribution of dark matter.

But… What is it made out of?

Long story short… We have no clue. We have a lot of ideas, but we aren’t quite sure of anything. But don’t worry, we are a master of making short stories long.

But there is one thing that most scientists agree on. That dark matter is made up of some sort of atomic particle. Some believe that this atomic particle is actually WIMPS or weakly interacting massive particles. What a fitting name right?

Others specifically think that dark matter is made out of neutralinos, axions, and photinos (all of these are WIMPS). Neutralinos are a type of a large neutrino, which is a large electrically neutral particle. Axions are also electrically neutral but are much smaller. A photino is, in short, the opposite of a particle of light (photon). These explanations are very obscure. Why? Because scientists haven’t actually proved the existence of these particles, so we don’t really know for sure if they exist.

But, most scientists agree that dark matter is made out of non-baryonic matter. Baryonic matter consists of all the matter we think is normal, solid, liquids, gasses - basically anything made out of protons and neutrons.

But, if you’re thinking that this is wacky, wait until you read the next section…

So then… What the heck is dark energy?

Dark energy is thought of as the complete opposite of gravity. (Instead of being pulled towards something, you are pulled away from something).To understand why scientists think that dark energy exists, we have to understand something really important about the universe.

The universe is constantly expanding. Most credit this expansion to the Big Bang; the prevalent theory about how our universe came to be. The idea is that the universe began with an extremely hot and dense point (so dense that protons and neutrons did not exist), that “exploded.” Aas this point inflated, temperature and density began to decrease, eventually resulting in everything we see today.

But this expansion from the Big Band is actually accelerating, rather than slowing down, like you would think. To explain this rapid acceleration, astronomers think that there is another form of energy, called dark energy, that is actually pushing cosmic objects apart rather than drawing them in closer. This dark energy is estimated to account for 68%-72% of the total energy of the universe. In fact, this energy dominates both everyday matter and dark matter!

So… what’s dark energy made out of? Well… we don’t really know. There are a lot of theories on what it can be made of. One of the prevailing theories is something called the cosmological constant. In short, this constant is a homogeneous energy density that causes the universe’s expansion to accelerate. 

This constant was actually introduced by Albert Einstein to provide a static universe solution rather than an accelerating one. But now it is used to explain the energy that causes the acceleration of the expansion of the universe.

What did we learn?

I hope you, my fellow readers, found this question easy to tackle. (If not, feel free to drop a comment and let me know how I can improve!) Today, we ventured into the "dark side" of science—quite literally. While we haven’t fully illuminated (see what I did there?) the mysteries of dark matter and dark energy, we’ve taken a meaningful step toward understanding them. Who knows? Maybe one day, you will be the one to unlock the secrets of the universe!