What is a brown dwarf?

A brown dwarf is a celestial object that is too small to sustain nuclear fusion in its core like stars do, but too massive to be classified as a planet. These objects are sometimes referred to as failed stars or substellar objects.

Brown dwarfs are relatively cool and dim compared to stars, which makes them difficult to observe. They were first theorized in the 1960s, but the first confirmed brown dwarf was not discovered until 1995.

Brown dwarfs have many characteristics similar to both stars and gas giant planets. They are composed mostly of hydrogen and helium, with a small amount of heavier elements. Unlike gas giant planets, brown dwarfs emit infrared radiation due to the heat generated during their formation.

Studies of brown dwarfs have contributed to our understanding of stellar formation and the formation of planetary systems. They also hold promise for research into the search for extraterrestrial life, as some theories suggest that they may be able to support habitable moons.

A brown dwarf is a substellar object that is not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in its core, unlike a main-sequence star. Instead, they have a mass between the most massive gas giant planets and the least massive stars, approximately 13 to 80 times that of Jupiter ( M J). However, they can fuse deuterium (2H) and the most massive ones (> 65 M J) can fuse lithium (7Li).

As brown dwarfs have relatively low surface temperatures, they are not very bright at visible wavelengths, emitting most of their light in the infrared. However, with the advent of more capable infrared detecting devices, thousands of brown dwarfs have been identified. The nearest-known brown dwarfs are located in the Luhman 16 system, a binary of L- and T-type brown dwarfs about 6.5 light-years (2.0 parsecs) away from the Sun. Luhman 16 is the third closest system to the Sun after Alpha Centauri and Barnard's Star.

Brown dwarfs are thought to form in the same way as stars, from the collapse of a large cloud of gas and dust. However, if the cloud is not massive enough, the core of the brown dwarf will not reach the temperature and pressure necessary to initiate nuclear fusion. As a result, brown dwarfs will gradually cool and dim over time, eventually becoming very faint and difficult to detect.

Brown dwarfs are an important part of the universe. They are thought to be much more common than stars, and they may play a role in the formation of planets. Brown dwarfs are also a valuable tool for astronomers, as they can be used to study the early stages of star formation.