Brown dwarfs and planets in dense environments
Stars in dense clusters, known as globular clusters, formed in very different conditions to the stars forming today. They formed at extremely high density and low metallicity, subject to intense irradiation by neighbouring stars. The search for brown dwarfs and planets in globular clusters can therefore tell us a lot about the physics of star and planet formation.
The talk at the bottom of this page concerning brown dwarfs and planets in dense environments is based on two papers: one on brown dwarfs and one on hot Jupiters.
Brown dwarfs are difficult to detect directly due to their low brightness, particularly at the distance of even the nearest globular clusters. However, brown dwarfs at sufficiently high density can pass close enough to stars to undergo a process called 'tidal capture'. This is a process by which they lose kinetic energy and form a short period sub-stellar companion. The companions may be detected to constrain the sub-stellar IMF in globular clusters.
Detecting planets that orbit far from their host star is challenging due to long orbital periods that require long baselines, lower amplitudes in radial velocity variations, and low probabilities of transiting their host star. However, short-period massive planets that orbit their host star on time-scales of < 10 days, known as hot Jupiters, are much easier to detect. In dense environments, these planets can form via eccentricity excitation and tidal circularisation.
