Brown Dwarf Evolution

If the fragmenting interstellar cloud collapses but has less than about 0.08 solar masses, the central temperature and density of the proto-star will never get high enough that hydrogen fusion can take place in a sustained, controlled manner.Such an object is a brown dwarf.

As it collapses, the brown dwarf will shine because it converts its gravitational energy to luminosity. It may burn hydrogen for a short period of time. Eventually, its collapse will be halted by electron degeneracy. Because it has no additional sources of energy, the brown dwarf will continue to radiate its internal heat until it fades out of view. It will then be a "black dwarf".

The diagram to the right shows the evolutionary paths in the HR diagram of three objects: a 0.07 solar mass brown dwarf (one almost massive enough to have made it as a star); a 0.01 solar mass brown dwarf; and a Jupiter-like object. The numbers associated with the tick marks on each path indicate the age, in years, since collapse began.

Suggested readings:

"The Search for Brown Dwarfs", Stevenson, D. 1991, Annual Reviews of Astronomy and Astrophysics 29 pp. 163.


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