What stellar objects result if a core never reaches the temperature needed for sustainable hydrogen fusion?
Answer
Brown Dwarfs
There exists a mass limit below which even the most intense gravitational contraction cannot generate enough heat in the core to initiate sustained hydrogen fusion, which is the defining characteristic of a true star. Objects falling below this threshold, specified as less than about $0.08$ times the mass of the Sun, fail to become stars. Instead, they become Brown Dwarfs. These sub-stellar objects do not power themselves through nuclear fusion; they shine only via the residual heat left over from their initial gravitational contraction, causing them to slowly cool down over immense timescales.
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