Planets versus Brown Dwarfs --- The First 20 Million Years

Details Planets versus Brown Dwarfs --- The First 20 Million Years Planets versus Brown Dwarfs --- The First 20 Million Years

Apr 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....12995w&link_type=abstract

EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #12995

Physics

Fluid Dynamics

Scientific paper

The formation and early evolution of a giant planet and a brown dwarf are compared. The giant planet is formed as the consequence of the accretion of a solid core and the subsequent capture of nebula gas, the brown dwarf results from the collapse of a Jeans-unstable Bonnor-Ebert sphere. For both models the grey equations of radiation fluid dynamics are solved in Eddington-approximation, with spherical symmetry and including a time-dependent convection model. Detailed non-ideal equations of state and opacities (including dust and molecules) are used. The planet's peak luminosity is attained during the rapid contraction phase that follows after the critical mass is reached. The respective maximum of the brown dwarf occurs early in its brief accretion phase. The luminosity maxima are separated by the time needed to grow the planets critical core resulting in different ages at corresponding contraction states. Both the planet and the brown dwarf do have partially radiative interiors at the beginning of their hydrostatic evolution. The planet becomes almost fully convective during the rapid contraction after the critical mass. The Bonnor-Ebert collapse produces an 0.05 {M_&sun;} young brown dwarf with a radiative interior, that extends to 2/3 of the radius, from beginning of its hydrostatic contraction phase to an age of 5 Ma. The onset of Deuterium burning makes the brown dwarf essentially fully convective. Deuterium energy production is sufficient to fully balance the surface energy losses and the brown dwarf is in thermal equilibrium for a few Ma (in the stellar structure sence). Hence there is the possibility of a Deuterium main-sequence. After about 10 Ma the global properties of the brown dwarf correspond to those of standard evolutionary models that do not account for the formation process.

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