The Birth of Giants â Bottom Up or Top Down?
Core Instability Most serious problem is long timescale needed to build a core and accrete massive atmosphere. Can be alleviated: • growing cores excite nearby planetesimals • planetesimals collide, produce small fragments • fragments are well coupled to gas which cools them dynamically • debris can be very efficiently accreted by cores Gas drag efficient Cores grind their food for better appetite ! Rafikov 2004 Gas drag inefficient
Core Instability NO accretion of collisional debris Kenyon & Bromley 2009 Accretion of collisional debris ON Can form runaway cores within 10 Myrs in disk somewhat more massive than MMSN