Physics of Substellar Objects Interiors, Atmospheres, Evolution

Abstract

All stars visible to the naked eye owe their momentary brightness to nuclear reactions occurring in their interior. While this certainly makes them jewels of the night skies, it will eventually lead them to a tragic end, in which they will explode to become either degenerate white dwarfs, neutron stars or black holes. Another, more numerous but barely visible population has chosen to lead a dull but quiet and almost eternal life: these are careful not to ever become dependent on hydrogen to shine. Some, in their youth, do burn less energetic substances as deuterium and lithium, but they rapidly get short of supply. As a consequence, they steadily cool and contract, retaining intact most of the elements that made them. These brown dwarfs and giant planets form an entirely new class of astronomical objects. They fill a gap between stars and the planets of our Solar System. Their study informs us on our origins, the formation of stars and planets. It can also help us to understand or test theories from high pressure physics, to atmospheric dynamics, tides, condensation and cloud formation...etc. The course focuses on some physical aspects related to the theoretical study of these substellar objects: I detail their hydrostatic evolution and how it is modeled, what we can learn from Jupiter, Saturn, Uranus and Neptune, how the atmospheres of brown dwarfs and giant planets are key to their appearance and cooling, what we can learn from the recent observations of brown dwarfs and extrasolar planets, and how this affects our view of planet formation.