The Formation of Massive Star Systems by Accretion
  Massive stars produce so much light that the radiation pressure they exert on
the gas and dust around them is stronger than their gravitational attraction, a
condition that has long been expected to prevent them from growing by
accretion. We present three-dimensional radiation-hydrodynamic simulations of
the collapse of a massive prestellar core and find that radiation pressure does
not halt accretion. Instead, gravitational and Rayleigh-Taylor instabilities
channel gas onto the star system through non-axisymmetric disks and filaments
that self-shield against radiation, while allowing radiation to escape through
optically-thin bubbles. Gravitational instabilities cause the disk to fragment
and form a massive companion to the primary star. Radiation pressure does not
limit stellar masses, but the instabilities that allow accretion to continue
lead to small multiple systems.
