Are brown dwarfs actually stars, and do they have fusion?
Brown dwarfs are stars that do not have enough mass to ignite stable fusion reactions. They simply cool and gravitationally contract. Some might say that they are not stars, because stars are defined to have stable nuclear reactions occurring in their core. But others would argue that this only a working definition of a star, which might need revision given the variety of objects out there like brown dwarfs, white dwarfs, neutrons stars, etc.
