  Aims: Revealing the fragmentation, infall, and outflow processes in the
immediate environment around massive young stellar objects is crucial for
understanding the formation of the most massive stars. Methods: With this goal
in mind we present the so far highest spatial-resolution thermal submm line and
continuum observations toward the young high-mass protostar NGC7538 IRS1. Using
the Plateau de Bure Interferometer in its most extended configuration at 843mum
wavelength, we achieved a spatial resolution of 0.2"x0.17", corresponding to
~500AU at a distance of 2.7\,kpc. Results: For the first time, we have observed
the fragmentation of the dense inner core of this region with at least three
subsources within the inner 3000 AU. The outflow exhibits blue- and red-shifted
emission on both sides of the central source indicating that the current
orientation has to be close to the line-of-sight, which differs from other
recent models. We observe rotational signatures in northeast-southwest
direction; however, even on scales of 500 AU, we do not identify any Keplerian
rotation signatures. This implies that during the early evolutionary stages any
stable Keplerian inner disk has to be very small (<=500 AU). The high-energy
line HCN(4-3)v2=1 (E_u/k=1050K) is detected over an extent of approximately
3000 AU. In addition to this, the detection of red-shifted absorption from this
line toward the central dust continuum peak position allows us to estimate
infall rates of ~1.8x10^(-3)Msun/yr on the smallest spatial scales. Although
all that gas will not necessarily be accreted onto the central protostar,
nevertheless, such inner core infall rates are among the best proxies of the
actual accretion rates one can derive during the early embedded star formation
phase. These data are consistent with collapse simulations and the observed
high multiplicity of massive stars.
