Do you know what dark matter really is?
Where did the idea of dark matter come from? Is it the result of casual discussions, complex mathematical constructions to justify some theory, or is it simply a reality in the universe?
Maybe explaining it will seem simpler than you may have thought at first, so let’s give it a try.
Imagine a star. A planet passes by it. The star attracts the planet by gravity, the planet deviates from its path and enters an orbit around the star. It goes at a speed of 300 X (kilometers, miles, … per second).
Now, imagine another planet that also approaches the star but enters the orbit at a greater distance from the star. Since it is further from the first planet, the star’s gravity acts with a lesser force, and it goes at a speed of 200 something.
The third planet is even further away from the star and the gravitational influence on it is even weaker, so it enters the orbit at a low speed, only 100 X.
It is precisely that third planet that interests us. It is far away and barely feeling the star’s gravity, so it moves slowly.
But what would happen if the star’s gravity is increased?
The star would then attract the planet more strongly, so it, that planet, would speed up its movement. So, the speed of the planet in orbit depends on the strength of gravity. The greater the gravity, the greater the speed of the planet.
Now take another example. You see a planet and measure that it is moving at a speed of 300. What will you conclude?
So, you will conclude that it is acted upon by a star of high gravity. And if the planet’s speed was much lower, you would conclude that the star is either of low mass or far away (because its gravity is weak).
And what would you conclude if you saw a fast planet, but the mass of the star is not enough to keep the planet in orbit?
Something, some force must act on the planet! Which one?
Well, only gravity can do it. In addition to gravity, there are also electromagnetic forces that act only on charged particles, nuclear weak and nuclear strong forces that do their work only within the limits of atoms. Only the gravitational force can move and restrain the stars and galaxies. It seems infinite, although it decreases with the square of the distance.
So you will conclude that some matter acts with its gravity on the planet even though you cannot see that matter. After all, you don’t even see the air, but you know that it exists and that it has some effect.
And that is it. We are convinced, based on observed facts, that there is some matter that we cannot see.
That’s why we call it dark matter.
It accelerates stars on the peripheries of galaxies and galaxies on the peripheries of galaxy clusters, and at the same time prevents stars and galaxies from drifting into space because of their high speed.
So, as things stand now, dark matter simply has to exist – there is no other solution. Everything that has been offered so far has not successfully answered the question of the acceleration of stars and galaxies at the rims of large structures and their holding together.
Dark matter, its existence, structure, composition, and everything else related to it, is one of the greatest mysteries of nature.
If dark matter really exists, then these questions are among the most important that science faces. If it does not exist, then physicists may have a more difficult task: to find an answer to the question of how it is possible for the universe to exist without dark matter.
