What is the common thread defining brown dwarfs, protostars, and stellar remnants as non-fusing objects?

Answer

Inability to maintain sustained hydrogen fusion ($ ext{}^1 ext{H} ightarrow ext{}^4 ext{He}$)

The fundamental requirement for an object to be classified as a true star is the ability to run the self-sustaining nuclear furnace where ordinary hydrogen is continuously converted into helium in the core. Brown dwarfs fail this because they lack the minimum required mass ($0.08 M_{ ext{SOLAR}}$). Protostars have not yet reached the ignition temperature due to still accreting mass. Stellar remnants (like white dwarfs, neutron stars, or black holes) have exhausted their fuel supply. Therefore, the common characteristic uniting these diverse non-luminous or post-luminous objects is the cessation or failure to initiate the necessary pressure conditions for indefinite $ ext{}^1 ext{H}$ fusion.

What is the common thread defining brown dwarfs, protostars, and stellar remnants as non-fusing objects?

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processstellarstarFusionnuclear