An Introduction to Brown Dwarfs

The field of brown dwarfs lies at the intersection of the much larger fields of stellar astrophysics and the emerging field of exoplanets.

In the 1960s, astrophysicists predicted a minimum mass to stars, below which objects do not become hot enough to fuse hydrogen into helium. These objects are now known as "brown dwarfs," and since 1995, thousands have been discovered. Current estimates are that the star formation process creates one brown dwarf for every six stars. Over time, brown dwarfs cool and fade, exhibiting atmospheric processes similar to planets, including chemistry, condensation, cloud formation, and weather. Worthy of study in their own right, brown dwarfs offer the opportunity to observe and test theories of star and planet formation, stellar evolution, and planetary atmospheres in ways that are otherwise impractical.

This book provides an introduction to brown dwarfs aimed at advanced undergraduates and beginning graduate students, supplementing stellar astrophysics or (exo)planetary science classes. It emphasises the key theoretical ideas and the main observational results that support those ideas. The first chapter is an introduction to the concept of brown dwarfs, their similarities and differences with stars and planets, and classification challenges. The second section examines brown dwarf atmospheres, with an emphasis on both understanding the key concepts and making use of the detailed models. The final major section addresses the formation of brown dwarfs, the initial mass function, and the related problem of brown dwarf multiplicity.