Astronomy Colloquium

The year 1995 was the annus mirabilis for substellar astronomy, with the discovery of both brown dwarfs and gas-giant exoplanets. In the 20+ years since, study of both classes of objects have flourished, with the discovery of thousands of these objects and a concomitant leap in characterizing their properties. Direct imaging has become a key method to study gas giants in their youth and has opened a new window to deepen our knowledge of both the exoplanet and brown dwarf populations.  I discuss how direct imaging studies have challenged our conceptions of
gas-giant formation and properties, as well as enriched our knowledge of substellar evolution and atmospheres.  I also show how our understanding of low-mass objects in the inner square arcsecond around bright stars is being advanced by wide-field surveys that mine the entire sky.  Finally, I present high-precision astrometry results that measure these objects' fundamental properties (luminosities, temperatures and masses) and thereby test the theoretical models common to all studies in the substellar regime.