Lobe Overflow as the Likely Cause of Pericenter Outburst in an SMBH
  Orbiter
  A very large lobe overflow event is suggested to explain the $0.^m4$
brightening observed in K band at pericenter passage of the star known as S2
that orbits the Galaxy's supermassive black hole (SMBH). Known observed
properties of S2 that contribute to lobe filling are 1) the enormous mass
ratio, $M_{SMBH}/M_{S2}$, 2) S2's fast rotation, and 3) S2's large orbital
eccentricity. Published estimates have given limiting lobe sizes of order 100
to 300 $R_\odot$ but, with S2's fast rotation taken into account, the computed
lobe size is much smaller, being compatible with either a main sequence OB star
or a stripped evolved star. An important evolutionary consideration that
predicts very large pericenter overflows is envelope expansion following mass
loss that is characteristic of highly evolved stars. Material removed by lobe
overflow at pericenter is replenished by envelope expansion as an evolved star
awaits its next pericenter passage. An observational signature of lobe overflow
for upcoming pericenter passages would be appearance of emission lines as the
ejected gas expands and becomes optically thin.
