Description: A brown dwarf is an object too low in mass to be a star but too high in mass to be a planet. Stars are fueled by hydrogen fusion in their cores. Brown dwarfs have internal temperatures that are too low to sustain hydrogen fusion. However, early in their lifetime brown dwarfs are able to briefly fuse deuterium, a heavier form of hydrogen. This deuterium fusion is used to distinguish brown dwarfs from planets but is hard to observe. Brown dwarfs typically have masses between 1.2% and 8% of the mass of the Sun (around 12–80 times the mass of Jupiter) and are roughly the same physical size as Jupiter. Young brown dwarfs have similar temperatures in their outer regions (effective temperature) to low mass stars (red dwarfs) but lacking internal heat sources they cool as they age, with some cooling to a few hundred degrees Celsius.

Related Terms:

• Hydrogen
• Hydrogen Fusion
• Jupiter
• Mass
• Planet
• Red Dwarf
• Effective Temperature
• Stellar Activity

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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