Andreas Burkert, Mark Schartmann, Christian Alig, Stefan Gillessen, Reinhard Genzel, Tobias Fritz, Frank Eisenhauer
The origin, structure and evolution of the small gas cloud, G2, is
investigated, that is on an orbit almost straight into the Galactic central
supermassive black hole (SMBH). G2 is a sensitive probe of the hot accretion
zone of Sgr A*, requiring gas temperatures and densities that agree well with
models of captured shock-heated stellar winds. Its mass is equal to the
critical mass below which cold clumps would be destroyed quickly by
evaporation. Its mass is also constrained by the fact that at apocenter its
sound crossing timescale was equal to its orbital timescale. Our numerical
simulations show that the observed structure and evolution of G2 can be well
reproduced if it formed in pressure equilibrium with the surrounding in 1995 at
a distance from the SMBH of 7.6e16 cm. If the cloud would have formed at
apocenter in the 'clockwise' stellar disk as expected from its orbit, it would
be torn into a very elongated spaghetti-like filament by 2011 which is not
observed. This problem can be solved if G2 is the head of a larger, shell-like
structure that formed at apocenter. Our numerical simulations show that this
scenario explains not only G2's observed kinematical and geometrical properties
but also the Br_gamma observations of a low surface brightness gas tail that
trails the cloud. In 2013, while passing the SMBH G2 will break up into a
string of droplets that within the next 30 years mix with the surrounding hot
gas and trigger cycles of AGN activity.
View original:
http://arxiv.org/abs/1201.1414
No comments:
Post a Comment