Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...

(Fig. 3.4), corresponding to approximately the virial temperature of the sink:
Tvir GMsinkmH
kBracc
10 4 K.
The mass of hot dense gas undergoes an equally smooth decline over the
next 1000 yr in the ‘no-feedback’ case. A minimal amount of dense gas is newly
heated after 1000 yr because there is no longer a dense disk structure entirely
surrounding the main sink. Most of the dense gas instead trails behind the
sink in the tidal tail, and the gravitational heating provided by the sink is now
imparted directly to the lower-density particles. Sink gravitational heating
thus halts the growth of the outer envelope, which we define to include all gas
particles at densities above 10 8 cm −3 as well as the sinks (solid blue line in
Fig. 3.3). The ‘heat wave’ travels beyond the disk at approximately the sound
speed, causing the decline in envelope mass beginning at around 2500 yr in
Figure 3.3, and reaching distances of > 7000 AU (see Figs. 3.4 and 3.5) by the
end of the simulation. At this time, heated gas thus resides almost entirely at
low densities (n < 10 9 cm −3 )
This disk and envelope evolution resembles that in Stacy et al. (2010),
particularly in that early gravitational heating by the sink caused the develop-
ment of a phase of hot and dense gas. However, the hot phase in Stacy et al.
(2010) fell mostly between densities of 10 8 and 10 12 cm −3 , and the mass of both
the envelope and total star-disk system showed a steady increase throughout
the simulation. In contrast, in our current ‘no-feedback’ case, the hot phase
lies mostly between densities of 10 6 and 10 9 cm −3 , and both the disk and
envelope decline in mass after 2000 yr. This difference between simulations
ultimately arises from the statistical variation in sink N-body dynamics, and
the corresponding response from the surrounding gas.
74