A Breakdown of The Idea of Dark Matter

Have you ever wondered if there was something more out there that was bigger than us? Ever imagine it being invisible? Maybe, but most likely not, right? Well, as science has theorized time and time again, there is another something out there. This something is Dark Matter. According to scientists, dark matter takes up about 25% of the universe. The rest is dark energy (which takes up about 70%( and visible matter (which takes up about 5%). It may sound like we know a lot about this thing we call Dark Matter, but in reality, we don’t. We basically know three things: There is something there, it interacts with gravity, and there is a lot of it.

You probably are wondering: “What is dark matter?”. Basically, it is an invisible substance that helps hold galaxies together. Let’s take a look at some history. During the 1960’s and 1970’s, astronomer, Vera Rubin, was observing spiral galaxies. You can learn a lot about galaxies by the way they spin. As she was observing them, she noticed something unusually strange. The galaxies were moving at alarmingly faster rates than predicted. In the 1600’s, Johannes Kepler discovered that the farther a planet is from the sun, the slower it orbits. Later, Newton put numbers to this and found equations to find the mass of the sun by finding it’s gravity. You cannot actually see the nebulae move, but you can measure their Doppler shift. Rubin expected that the nebulae would move in a similar pattern to solar systems. But what she found was that, even on the outskirts of the galaxies, the speed was uniform or even faster. When looking at galaxies, you can clearly see fewer stars on the outsides of the galaxies. So the only way to make the equations work, was if there was more matter. Scientists dubbed this, Dark Matter.

Over the years, experiments have only confirmed Dark Matter. Scientists listed everything they could think it could be. They thought of cold gas, dust, and dead stars. They thought of rogue planets and even weird subatomic particles. These particles were predicted to exist in quantum mechanics theories but never seen before. The scientists tested this dark matter to see if it gave off anything that normal matter would give off. Nothing was found, but they eventually crossed off everything on the list. The only thing left were those crazy subatomic particles.

There are many theories on what dark matter actually is. Dark matter could not exist, for one. Many scientists believe it doesn’t exist, but the math just does not add up without it. It could be MACHO’s (MAssive Compact Halo Objects). These include black holes, brown dwarfs, and neutron stars. Yet, there is too much dark matter for it to all be MACHO’s. It could be Neutrinos, which are small subatomic particles that don’t react with normal matter. 10’s of 1000’s of these go through you every second. However, they move faster than the speed of light, which would make them extremely hot. Also, it has been proven that dark matter moves much slower than the speed of light.

The next two theories are the most probable. Dark matter could actually be a subatomic particle called an Axion. We have never actually been able to observe axions, however, which makes it very difficult to acquire evidence to back up this theory. However, axions have all the same properties as dark matter and they have mass, so a huge cloud of them would account for all the matter. They do not emit light and they do not interact with normal matter. They pass right through it so it could, potentially, envelop a galaxy. Another possible candidate is WIMP’s. They are a form of cold dark matter but are bigger and more likely to react with normal matter than axions. We haven’t been able to find anything definitive about them yet, and nothing has been able to detect them.

All theories aside, how do we know it is there? Einstein discovered the theory of general relativity. This says that space and time are like a woven fabric called space-time. Gravity sits on that fabric which distorts it. Such as a bowling ball on a mattress, if you took a marble and rolled it by, it’s path would bend. We can tell how much mass is in the galaxy by gravitational lensing. Basically, if you have a galaxy directly behind another, the light from the farthest one, would be bent by the gravity of the closest one. This can show where, and how much matter there is. When we look at this, there is too little matter that we can see.

Another way we know is by looking at the Bullet Cluster. In clusters, there is gas in between the galaxies. The Bullet Cluster is two clusters that smacked into each other. When they did, the gasses would smack into each other becoming very hot and giving off x-rays. Before this scientist calculated the amount of mass in each of the clusters. Then, with the Chandra x-ray observatory, they measured where the x-rays were. The x-rays were in the middle of the clusters, as expected, but the rest of the matter was on the edges the clusters. This matter you could not see, therefore it must be dark matter.

Many people have tried to explain it without dark matter, but the truth is, you can’t. Dark matter can’t be detected, which is why it is so difficult to find. When we look at the timeline of our universe, we realize that galaxies would have had a really hard time forming without this matter. Dark matter is needed in the universe for anything to work. Without it, galaxies would fly apart.

We may not know a lot about dark matter. And we may know more about what it isn’t than what it is. But we do know, that it is invisible. However, it does have mass and clouds of it would have a substantial amount of mass. We also know it is massive and has an impact on the gravity in galaxies. However, it is invisible to not only the human eye but to all technological equipment. It also has no interaction with light or the electromagnetic force whatsoever. Dark matter may be a very confusing subject, but it’s important. We only, really, know three things: There’s definitely something there, it has a huge effect on gravity, and there is a whole lot of it.

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