What is Baryonic Matter?
Baryonic matter is the "ordinary" matter we interact with daily. It consists primarily of baryons, which are subatomic particles composed of three quarks. The most common baryons are protons and neutrons, which form the nuclei of atoms. Essentially, everything you can see, touch, or measure directly – from a grain of sand to an entire galaxy – is made of baryonic matter.
Key Components and Definition
The definition of baryonic matter hinges on baryons, a class of hadrons. Protons (two up quarks, one down quark) and neutrons (one up quark, two down quarks) are the stable baryons that constitute atomic nuclei. Electrons, while fundamental to forming atoms, are leptons, not baryons. Therefore, while they are part of "ordinary matter" (atoms), electrons themselves are not baryonic.
Baryonic Matter in the Universe
In the vastness of the cosmos, baryonic matter accounts for only about 4-5% of the total mass-energy content of the universe. The majority of the universe is composed of dark matter (around 27%) and dark energy (about 68%). This relatively small fraction of baryonic matter forms all the visible structures, including stars, planets, dust, gas, and celestial bodies we observe.
Distinction from Other Forms of Matter
Baryonic matter is crucial to differentiate from other types of matter in cosmology. Unlike dark matter, which does not interact with light and is detected only through its gravitational effects, baryonic matter emits, absorbs, and reflects light. This interaction with electromagnetic radiation allows us to observe and study it directly, forming the basis of observational astronomy.