Accretion Centers Induced in a Molecular Cloud Core After a Penetrating Collision - Selected Topics of Computational and Experimental Fluid Mechanics - page 479

collapse, see for instance Arreaga-Garcia et al. ( 2014 ) and references there in.
Recently, Higuchi et al. ( 2014 ) presented line emission observations of the core
G.0253

0.016 with the Atacama Large Millimeter Array (ALMA) and proposed
that this dense cloud may have formed due to a collision between two dissimilar
clouds.
In this paper we consider a system of two gas spheres, the first one being the target
core and is constructed in a similar way to that originally suggested by Whitworth
and Ward-Thompson ( 2001 ), as an empirical model to study the collapse of the well
observed core L1544. The latter is unstable and would collapse toward a binary
system of protostars. The second and smaller gas sphere that we will call the bullet
is directed towards the target core. We are interested in investigating what happens
in this case.
Whether a penetrating collision does or does not help the fragmentation of the
target gas core is the main aim of this study. The target core is additionally considered
to be in counterclockwise rigid body rotation around the Z axis.
There are three physical processes participating in a gas collision: (i) the
self-gravity of the target core; (ii) the flow of particles of the bullet core, which
tend to diffuse within the target core, and (iii) the friction due to the viscosity of the
gas. The pre-collision velocity determines which of these physical process is more
important than another in a particular simulation, and therefore it determines the fate
of the collision system.
It is noteworthy that Anathpindika ( 2009 ) has also simulated collisions between
two clouds, considering an impact velocity within the Mach 25-35 range, and also
that dissimilar collision models were also considered by Anathpindika ( 2010 ). But
all their pre-collision clouds are initially in hydrodynamical equilibrium since they
were modeled as Bonnor-Ebert spheres.

+

2 The Colliding Cores

We consider two dissimilar spherical cores which undergo a head-on collision, as
illustrated in Fig. 1 . The initial position (in rectangular coordinates ( X , Y , Z ) )ofthe

mass center (MC) of the target core is located at X TC = ( 0 , − R 0 , R 0 ) , while the MC

for the onrushing core is located at X OC = ( 0 , R 0 , R 0 ) . As previously mentioned,

R 0 is the initial radius of the target core.
The pre-collision velocity V app (or impact velocity) is defined as the translational
velocity given to all the particles of the bullet core, in such a manner that its MC
moves with the velocity V OC = ( 0 , − V app , 0 ) . The target core MC is initially at rest,

that is V TC = ( .

All the models of this paper deal with a gas sphere of radius R 0 =

0 , 0 , 0 )

10 16 cm,

8 . 0 ×

10 − 18 g cm 3 . The total mass in the target and with an average density ˁ ave = 3 . 0 × /

core is M 0 = 8 M . It should be emphasized that Whitworth and Ward-Thompson

( 2001 ) suggested these parameters for investigating the L1544 core's fate.