I can not believe it took so much time to finally write about dark matter since I knew about it such a long time and thought that I should write about it some time.
Now because dark matter has to do a lot with gravity (and only gravity) then I just have to share with you this meme:
OK, enough fun for now, lets see what this dark matter is.
How did we find it?
Once upon a time one great scientist was born and her name was Vera Rubin. It happened in kingdom (federal republic) far far away, over one big ocean and no mountains. Vera wanted to be astronomer since her 10 years. When she signed up for some school they asked her if she does not want to draw space objects since she liked to draw, this was because in 40s female scientists were not very common.
Finally she was able to start to work and with new age of better telescope she began with huge observation. Most people used those telescopes to look at active cores of galaxies and such exciting places but Vera with her colleague Ford rather observed the outskirts of galaxies and they saw very interesting thing, these outskirts were moving way too far.
As object get away from the thing they orbit (as in our Solar System) they tend to orbit slower.
- Mercury 47.36 km/s
- Venus 35.020 km/s
- Earth 29.783 km/s
- Mars 24.077 km/s
- Jupiter 13.050 km/s
- Saturn 9.638 km/s
- Uranus 6.795 km/s
- Neptune 5.432 km/s
Pluto 4,666 km/s(oops not a planet :D)
So as you see the orbit speed really decreases, this is because there is lower force of gravity so the planet does not need to be so fast to make these forces equal.
In galaxies this should happen too but it does not!
Now here comes the theory of dark matter which is spread over whole galaxies and there is tremendous amount of it making those stars in the outskirts to go faster than they should.
There are only 4% of ordinary matter the one which we know about a lot.
21% is dark matter and 75% is dark energy as you can see on the next picture:
The only thing we know about dark matter is that it interacts with ordinary matter through gravity. We can measure this and measure how much and where it is, also we know that it does not tend to create some piles like normal matter so it seems that there are no dark matter stars. As Sean Carroll says in his book Particle at the End of Universe, dark matter is a clear example of something beyond the standard model of particles.
 At first I wrote collieg instead of colleague, it took me a long time to figure the spelling out even using the corrector in Chrome, I think this will make one of my friends really really happy!
19.1.2016 I made second part so click HERE to read more about dark matter.