Substellar object

[5] Substellar objects like brown dwarfs do not have enough mass to fuse hydrogen and helium, hence do not undergo the usual stellar evolution that limits the lifetime of stars.

A substellar object with a mass just below the hydrogen-fusing limit may ignite hydrogen fusion temporarily at its center.

Apart from these sources, the radiation of an isolated substellar object comes only from the release of its gravitational potential energy, which causes it to gradually cool and shrink.

Infrared spectroscopy can detect the distinctive color of water in gas giant size substellar objects, even if they are not in orbit around a star.

[7] William Duncan MacMillan proposed in 1918 the classification of substellar objects into three categories based on their density and phase state: solid, transitional and dark (non-stellar) gaseous.

Earth and space bound observatories observe Gliese 229 and its companion, which is perhaps 20–40 Jupiter masses in size [ 9 ]