Dark matter is the most mysterious and inert substance in the universe. Its gravitational effects explain the rotation of galaxies, the movement of clusters, and the largest-scale structures in the entire universe. But on a smaller scale, it is too small to affect the movement of the solar system, the matter of the Earth, or the origin and evolution of man. That being said, the gravity that dark matter provides is absolutely essential for the raw ingredients that make up life like us and a planet like Earth. Without dark matter, there could be no life in the Universe at all.
Stars produce 100% of the light we see in the universe, but only 2% of its mass. When we look at the motions of galaxies, clusters, and more, we find that the amount of gravitational mass outweighs the stellar mass by 50 times. One would think that other types of ordinary matter could explain this difference. After all, we discovered many other types of matter in the universe besides stars:
- the remains of a star like white dwarfs, neutron stars and black holes;
- asteroids, planets and other objects, the mass of which is too small to be stars;
- neutral gas in galaxies and the space between them;
- dust blocking light and foggy regions;
- ionized plasma, which is abundant in the intergalactic medium.
All of these forms of ordinary matter - or matter that originally consisted of the same things that we are: protons, neutrons, and electrons - do contribute. Gas and plasma, in particular, contribute more than the sum of all the stars in the universe. But even if we add all these components together, we get only 15-17% of the total amount of matter that is needed to explain gravity. For the rest of the motion that we see, we need a form of matter that not only differs from protons, neutrons and electrons, but also does not correspond to any known particle of the Standard Model. We need some kind of dark matter.
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A small group of scientists are against adding some kind of invisible source of mass, but for changing the laws of gravity. Such a model has difficulties, including the inability to reproduce the full set of observations, including the movement of individual galaxies in clusters, the cosmic microwave background, collisions of galaxy clusters, and the giant cosmic network of the observed large-scale structure of the Universe. There is also another important piece of evidence that points to the existence of dark matter. You will be surprised, but this is our existence.
It will surprise you that we not only need dark matter to explain astrophysical phenomena like galactic rotation, the movement of clusters and their collisions, but also to explain the very origin of life.
To understand why, you need to remember that the Universe began with a hot and dense state - the Big Bang - when everything was in the form of a practically homogeneous sea of separate, free, high-energy particles. As the Universe cooled and expanded, protons, neutrons and the lightest nuclei (hydrogen, helium, deuterium and a little lithium) were formed, but nothing else. It was only tens or hundreds of millions of years ago that this matter collapsed into regions dense enough to form stars and, finally, galaxies.
All this would have happened, albeit in a slightly different way, with or without dark matter. But for the elements necessary for life to proliferate in abundance - carbon, oxygen, nitrogen, phosphorus, sulfur - they must be smelted in the cores of the most massive stars in the universe. It makes us neither hot nor cold; in order for them to form solid planets, organic molecules and life, they first need to throw these heavy atoms into the interstellar medium, where they will again become stars, already by the next generations. This requires a supernova explosion.
We watched these explosions in great detail and know, in particular, how quickly this material is ejected from the stars in their death throes: at thousands of kilometers per second. (The remains of the supernova Cas A ejected material at speeds of 5000 and even 14,500 km / s!). While this number may seem small, especially given the speed of light, keep in mind that our own star is orbiting in the Milky Way at only 220 km / s. If the Sun rotated at least three times faster, we would already be outside the gravitational pull of our galaxy - we would be thrown out.
Supernova remnants eject heavier matter, but thanks to the powerful gravitational pull of a diffuse, elongated dark matter halo, we will be holding most of this mass inside our own galaxy. Over time, the matter will return to normal regions rich in normal matter, form neutral molecular clouds and form the basis for subsequent generations of stars, planets and, most interestingly, organic molecular combinations.
But without the additional attraction of the massive dark matter halo surrounding the galaxy, the vast majority of material ejected from a supernova would leave the galaxy forever. It will always float in the intergalactic environment, but it will never become part of future generations of stellar systems. In the Universe without dark matter, we would have stars and galaxies, but the planets would be only gas giants, there would be no solid worlds, no liquid water and life either. Without the abundance of heavy elements supplied by generations of massive stars, molecular-based life would never exist.
It turns out that the massive halo of dark matter that surrounds our galaxy, which allowed the emergence of life based on carbon, which chose Earth as its home - or something else - is worth thanking for all this. As we delve deeper and deeper into the principles of the universe, we understand that dark matter is absolutely necessary for the appearance of life. Without it, there would be no chemistry, complex elements, biology, solid planets, life - and us.
ILYA KHEL