Brown dwarfs are objects formed in the same way as stars, from the same material as stars, but which do not have the critical mass required to burn nuclear fuel like stars. That critical mass is about seven hundredths of a solar mass (or equivalently seventy Jupiter masses).

The existence of brown dwarfs was first proposed by Dr Shiv Kumar in 1963, though the name "brown dwarf" was only coined some years later by Dr Jill Tarter (now more widely known for her work on the Search for Extra-terrestrial Intelligence). The first bona fide brown dwarf discoveries were announced in 1995, at the same meeting in Florence, Italy, where the first extra-solar planet was announced. In the years since, approximately 50 more brown dwarfs have been discovered.

Theorists have predicted the presence of dust in some cool brown dwarfs for several years, however the recent discovery that brown dwarfs also rotate rapidly with periods of hours, has highlighted the likelihood that brown dwarfs may show weather patterns like the giant planets in our own Solar System.

rb@aaoepp.aao.gov.au 7 May 1999