The theory of globulettes: candidate precursors of brown dwarfs and free-floating planets in H ii regions

摘要: Large numbers of small opaque dust clouds - termed ‘globulettes’ by Gahm et al have been observed in the Hii regions surrounding young stellar clusters. With masses typically planetary (or low mass brown dwarf) regime, these objects are so numerous some (e.g. Rosette) that, if only a fraction them could ultimately collapse, then they would be very signicant source free oating planets. Here we review properties globulettes and present theoretical framework for their structure evolution. We demonstrate that interior is well described pressure conned isothermal Bonnor-Ebert sphere mass{radius relation (M / R 2:2 ) systematic consequence column density threshold below which components globulette not identied. also nd with this stable against collapse within regions. follow assuming detached from tips pillars protruding swept up shell borders expanding region produce model dynamics, nding will eventually impact shell. derive an expression time it takes to do show dissipation energy via cooling allows all survive encounter escape into wider ISM. Once there ambient drops disperse on timescales around 30{300 kyr should observable using ALMA out distances order parsec. Since stable, route might still form dwarfs or planets during collision other violent perturbative event.