<P> Atoms form about 4% of the total energy density of the observable Universe, with an average density of about 0.25 atoms / m . Within a galaxy such as the Milky Way, atoms 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, a region of highly ionized gas, 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 atoms are concentrated inside stars and the total mass of atoms forms about 10% of the mass of the galaxy . (The remainder of the mass is an unknown dark matter .) </P> <P> Electrons are thought to exist in the Universe since early stages of the Big Bang . Atomic nuclei forms in nucleosynthesis reactions . In about three minutes Big Bang nucleosynthesis produced most of the helium, lithium, and deuterium in the Universe, and perhaps some of the beryllium and boron . </P> <P> Ubiquitousness and stability of atoms relies on their binding energy, which means that an atom has a lower energy than an unbound system of the nucleus and electrons . Where the temperature is much higher than ionization potential, the matter exists in the form of plasma--a gas of positively charged ions (possibly, bare nuclei) and electrons . When the temperature drops below the ionization potential, atoms become statistically favorable . Atoms (complete with bound electrons) became to dominate over charged particles 380,000 years after the Big Bang--an epoch called recombination, when the expanding Universe cooled enough to allow electrons to become attached to nuclei . </P> <P> Since the Big Bang, which produced no carbon or heavier elements, atomic nuclei have been combined in stars through the process of nuclear fusion to produce more of the element helium, and (via the triple alpha process) the sequence of elements from carbon up to iron; see stellar nucleosynthesis for details . </P>

What state of matter has the electrons separated from the nuclei of the atoms