Brown dwarfs are celestial objects that are larger than planets but smaller than stars. They form in a similar way to stars, through the gravitational collapse of gas and dust, but they do not have enough mass to sustain nuclear fusion in their cores. This means they cannot shine like true stars, making them difficult to detect. Typically, brown dwarfs have masses between about 13 and 80 times that of Jupiter. They emit heat and light primarily from the energy released during their formation, rather than from fusion. As a result, they gradually cool and fade over time, becoming less visible in the universe.