The Gravity Collaboration detected a near-infrared hotspot moving around Sgr A* during the 2018 July 22 flare .
They fitted the partial loop the hotspot made on the sky with a circular Keplerian orbit of radius \simeq 7.5 r _ { g } around the supermassive black hole ( BH ) , where r _ { g } is the gravitational radius .
However , because the hotspot traversed the loop in a short time , models in which the hotspot tracks the motion of some fluid element tend to produce a best-fit trajectory smaller than the observed loop .
This is true for a circular Keplerian orbit , even when BH spin is accounted for , and for motion along a RIAF streamline .
A marginally bound geodesic suffers from the same problem ; in addition , it is not clear what the origin of an object following the geodesic would be .
The observed hotspot motion is more likely a pattern motion .
Circular motion with r \simeq 12.5 r _ { \mathrm { g } } and a super-Keplerian speed \simeq 0.8 c is a good fit .
Such motion must be pattern motion because it can not be explained by physical forces .
The pattern speed is compatible with magnetohydrodynamic perturbations , provided that the magnetic field is sufficiently strong .
Circular pattern motion of radius \sim 20 r _ { g } on a plane above the BH is an equally good alternative ; in this case , the hotspot may be caused by a precessing outflow interacting with a surrounding disk .
As all our fits have relatively large radii , we can not constrain the BH spin using these observations .