Baryonic matter Dark matter

baryons (protons , neutrons) make ordinary stars , planets. however, baryonic matter encompasses less common black holes, neutron stars, faint old white dwarfs , brown dwarfs, collectively known massive compact halo objects (machos). ordinary, hard see, matter explain dark matter.

however multiple lines of evidence suggest majority of dark matter not made of baryons:

sufficient diffuse, baryonic gas or dust visible when backlit stars.
the theory of big bang nucleosynthesis predicts observed abundance of chemical elements. if there more baryons, there should more helium, lithium , heavier elements synthesized during big bang. agreement observed abundances requires baryonic matter makes between 4–5% of universe s critical density. in contrast, large-scale structure , other observations indicate total matter density 30% of critical density.
astronomical searches gravitational microlensing in milky way found @ small fraction of dark matter may in dark, compact, conventional objects (machos, etc.); excluded range of object masses half earth s mass 30 solar masses, covers plausible candidates.
detailed analysis of small irregularities (anisotropies) in cosmic microwave background. observations wmap , planck indicate around five-sixths of total matter in form interacts ordinary matter or photons through gravitational effects.




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