Baryonic matter

Baryonic matter is matter made chiefly of baryons, especially protons and neutrons, and includes familiar objects such as stars, gas, and dust.

Baryon: A composite subatomic particle made of three quarks, including protons and neutrons. Baryonic matter is named for this particle family.
Big Bang nucleosynthesis: The early-universe formation of light atomic nuclei, mainly hydrogen and helium isotopes. It established the primordial mix of nuclei in baryonic matter.
Dark matter: Matter inferred from gravitational effects that does not emit, absorb, or reflect enough light to be detected directly. Unlike baryonic matter, most dark matter is not made of known atomic constituents.
Baryon acoustic oscillations: A pattern of density variations in matter imprinted by sound waves in the early universe. Their present-day scale traces the early interaction of baryons and radiation.
Proton: A positively charged baryon found in atomic nuclei and the nucleus of ordinary hydrogen. Protons supply the nuclei in hydrogen, the universe’s most abundant element.
Recombination (cosmology): The epoch when electrons combined with nuclei to form neutral atoms in the early universe. Neutral atoms let photons travel freely through formerly opaque baryonic gas.
Antimatter: Matter composed of antiparticles, which have the opposite charges and quantum numbers of corresponding particles. Its scarcity relative to baryonic matter is a central cosmological puzzle.
Cosmic baryon budget: An accounting of ordinary matter across stars, gas, and other cosmic structures. It tracks where the universe’s baryonic matter is observed or remains difficult to detect.
Neutron: An electrically neutral baryon found in most atomic nuclei. Neutrons join protons in the nuclei of most elements.
Star formation: The process by which dense regions of interstellar gas collapse to form stars. Gravitational collapse gathers diffuse baryonic gas into luminous objects.

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