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10th of March 2023
Spiral arms around a high mass proto-star
by Burns et al.
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.

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