3 years ago

The Birth of Giants – Bottom Up or Top Down?

The Birth of Giants – Bottom Up or Top Down?


Gravitational Instability Convection • Boss (2004) suggested that convection may cool disk midplane faster than radiation thus leading to fragmentation • Unlikely since cooling in one period requires moving material up and down with close to sonic velocities • In addition gas would inevitably cool adiabatically as it rises • Photosphere would still be cold – cooling time long (Cassen 1993; Rafikov 2007) Slow photospheric cooling is a bottleneck making cooling time long and fragmentation leading to planet formation unlikely

Gravitational Instability External Irradiation. • Disk can remain gravitationally unstable in the presence of external irradiation • Irradiation suppresses fragmentation • Fragmentation is possible only at high mass accretion rates • Relevant in the earliest phases of disk formation, far from the star (> 100 AU) Rafikov 2009

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