The Universe is an oscillator
If we analyze the picture of the Universe, we find two energetic extremes.
From the entire matter, it is estimated that 10% is bright and hot – kinetic energy (galaxies and stars). and 90% is cold and without light – potential energy (planets, asteroids, meteorites, powder and dust). From the dynamic point of view, the hot, bright matter, with repulsive forces, dissipates. The cold, dark matter, with attraction forces, gathers together.
In both cases, the matter is made of the atoms of the elements. The question is how and where do these elements compose? There an assumption, that is more or less accepted, according to which, the elements are elaborated within the core of the stars. We are facing the dilemma “The egg or the hen”. What was first? The kinetic or the potential energy? The stars or “the rocks”? 
If we overcome this dilemma, it is possible to find “the laboratory of the elements” and we will know how the cosmic bodies were formed. At an energetic extreme, the elements decompose, at the other, the elements compose themselves. Decomposition means radioactivity. Composition is the reverse of radioactivity. Decomposition emits radiation. Composition receives photons! In stars there are radioactivity and radiation emissions. Here the elements decompose themselves! It results that the composition reactions take place in the intergalactic space, where the temperature is almost absolute zero and thus, radioactivity is lacking. It is difficult to imagine the composition phenomena. We still can make suppositions. Here, close to zero temperature, the atoms don’t emit radiation, but receive photons. If they don’t emit radiations, it means they neither absorb it! Why? They don’t have enough kinetic energy!  Absolute zero = kinetic energy 0!
What happens to the photon in these circumstances? At the impact with an atom, the photon “freezes”! it becomes hydrogen, or it links its electrical polarities with the electrical polarities of the atom - the atom includes a nucleon. 
Thus the stable elements are formed, including the artificial ones. A real atoms crop!
We notice the alternance of equivalent energy, photon–nucleon (energy–mass).
The kinetic energy unit wihtout mass became potential energy unit (mass unit).
The Universe is an oscillator, between the kinetic energy and the potential energy!
Now, we can talk about the formation of cosmic bodies. This “cold matter” gravitationally gathers in a sphere, in its center instability, radioactivity, high temperatures, abundant radiations (explosion?) occur and it becomes the nucleus of a galaxy or a star. The rotation movement forms the inertial belt and the magnetic field. These phenomena gather the cold matter on large surfaces, in the equatorial rotation plan. The matter gathers in rings or spiraled arms that will gather, forming stars or planets, according to the mass of the gathering matter. Now, we know why do the Sun and the planets have heavy and radioactive elements in their centers, why is Jupiter a special planet, why does the ring of asteroids exist between planet Mars and Jupiter in the Solar System, why are there rings around some planets, etc.