Dark Matter

Episode #4 of the course “Strangest Things in Space”

Dark matter is the second biggest component of our universe, making up close to 27%. The reason dark matter is called “dark” is because it does not interact with light in any way. In fact, the only way in which dark matter interacts with the rest of the universe is through its gravity.

Since we’re only able to see things that interact with light, how do we know dark matter exists, and how do we know it comprises 27% of the universe? Because of its interaction with other things that we can see, much like how we know wind exists.

In 1933, Swiss astronomer Fritz Zwicky noticed that two galaxies were orbiting each other faster than they should be. Well, faster than they should be given the amount of gravity he could observe. This was the first indication that there needed to be additional gravity being created by an additional mass that he could not see. He called this invisible mass dark matter. This missing mass problem exhibits itself in a number of other phenomena, further supporting the existence of dark matter.

The answer to the question of what dark matter actually is still unknown. Some of it is probably black holes, and some of it is probably WIMPs (weakly interacting massive particles), but by and large, the question of what dark matter is still trying to be discovered. What we do know is that something else is out there besides the universe we can see. In fact, the visible universe – that is, our planet, our solar system and galaxy, all other galaxies and stars – all add up to only 5% of the universe. As you know, dark matter accounts for another 27%, but the biggest component of all is the equally-mysterious dark energy which makes up a whopping 68% of the universe.

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