|
High-mass protostars (with masses greater than 8 solar masses) are
thought to gain the majority of their mass via short, intense bursts
of growth. This episodic accretion is thought to be facilitated by
gravitationally unstable and subsequently inhomogeneous accretion
disks, but observational evidence has been difficult to obtain.
Following its 2019 accretion burst, a heatwave driven by a burst of
radiation propagated outward from the high-mass protostar
G358.93-0.03-MM1. The southern hemisphere Long Baseline Array was
used with other VLBI (Very Long Baseline Interferometry) arrays to
trace the increasing disk radii as the heatwave propagated outward, by
tracking methanol maser emission at 6.7 GHz over six epochs.
Burns et al. have reported the discovery of a Keplerian accretion disk with a
spatially resolved four-arm spiral pattern around G358.93-0.03-MM1.
The figure above shows the methanol maser spotmaps of the
combined six-epoch data sets centred on the G358-MM1 position. The
black line indicates the direction of largest velocity gradient to
which the position-velocity cut was taken. The spiral arms identified
in this work are plotted as thick grey lines. This result positively
implicates disk accretion and spiral arm instabilities into the
episodic accretion high-mass star formation paradigm.
|
