A cloud of interstellar gas and dust that the stars and planets originate from differs from similar clouds in quantity, composition, and location of the matter it is made of, all of which depend on the events that made it so. Protomatter consisted of elementary particles that soon evolved in their composition into hydrogen and helium atoms. Soon, all known matter took the form of elementary particles and helium and hydrogen atoms. The compression of large amounts of helium gas atoms led to the transformation of the simplest atomic structures into more complex ones. The process by which such transformation occurs is called – fusion. Fusion releases energy, and one form of that energy is light. Clusters of matter in which atomic fusion and the release of energy and light occurred are known to us as stars. The processes in a star, and thus its future and life span, depend on the quantity of matter that began to compress under the influence of gravity. Conversion of atoms, from those with a lower atomic weight to those with a higher one, requires energy. It is provided by the gravitational force of all the atoms in a star, meaning that energy is limited by the mass of a star. In lighter stars, the fusion process is slower and ends with atoms of lower atomic weight. Heavier stars extend the fusion process to the atomic weight of iron, which will be the core of such a star. At this point, the fusion process encounters physical laws that apply to heavier atomic nuclei. However, if the mass of star material is sufficient, the process of fusion into heavier elements continues. The specific characteristic of this phase is that the reactions in the core of a star occur so intensively that they lift the outer layers of the star and disperse them in a titanic explosion that we call a supernova. The huge gas envelope, thrown into the surrounding space by the star’s explosion, expands at a high speed and contains material sufficient for the creation of several stars as big as our Sun. Such an envelope expands for about half a million years and draws in the thin interstellar material. In this way, the interstellar material is enriched with atoms of higher atomic weight. Furthermore, when the gas envelope, formed in the supernova explosion, comes across large amounts of interstellar material, its energy will cause a compression of that material and thus initiate the process of creating new stars and planetary systems. Without these external factors, clouds of interstellar gas are exceptionally stable since the pressure of atoms moving at high speeds within the cloud prevents the gravitational attraction between atoms, which tends to compress the cloud. Our Sun was also created by the compression of the interstellar gas envelope due to a supernova explosion. The group of stars closest to us and their planetary systems were also formed from the same cloud and for the same reason, by splitting into smaller units.
Planetary systems are formed from the particles of dust that, along with the gas cloud, are in the orbit of a star that is being formed. Planets closer to the Sun are called rocky planets because of their composition. Planets in the outer part of the Solar System are composed almost entirely of gases, but pressurized to the extent that they became liquid. Interstellar material is also enriched in the processes related to the late stages of the Sun’s development when it becomes a red giant. When the elements of higher atomic weights, carbon and oxygen, are formed in the core of the Sun, after the last cycle of nuclear reactions in it, the mass of the Sun becomes insufficient for the fusion process to continue. The Sun “burns out” and gravity overpowers the forces opposing it. The Sun pulsates, expanding and contracting. In the end, the Sun will expel its atmosphere in the form of one or several concentric shells of gas. In this way, the Sun will expel half of its mass. Apart from the elements that reach interstellar space by being produced in stars and supernovae, some heavier elements may have been formed by the energy released at the very moment of the supernova explosion.
The entire cosmos, almost everywhere, consists of 99% hydrogen and helium. Every thousandth star ends up as a supernova (explodes). Supernovae are a source of cosmic radiation. They expel electrons and protons of extremely high velocities into space.