structural:reformatting
Origin and current state

Baryonic matter forms about 4% of the total energy density of the observable universe, with an average density of about 0.25 particles/m (mostly protons and electrons). Within a galaxy such as the Milky Way, particles have a much higher concentration, with the density of matter in the interstellar medium (ISM) ranging from 10 to 10 atoms/m. The Sun is believed to be inside the Local Bubble, so the density in the solar neighborhood is only about 10 atoms/m. Stars form from dense clouds in the ISM, and the evolutionary processes of stars result in the steady enrichment of the ISM with elements more massive than hydrogen and helium.

Up to 95% of the Milky Way's baryonic matter are concentrated inside stars, where conditions are unfavorable for atomic matter. The total baryonic mass is about 10% of the mass of the galaxy; the remainder of the mass is an unknown dark matter. High temperature inside stars makes most "atoms" fully ionized, that is, separates all electrons from the nuclei. In stellar remnants —with exception of their surface layers—an immense pressure make electron shells impossible.