Accretion Centers Induced in a Molecular Cloud Core After a Penetrating Collision - Selected Topics of Computational and Experimental Fluid Mechanics - page 480

Fig. 1 The initial geometry
of the colliding cores

The dynamical properties of the initial distribution of particles are commonly
characterized by the thermal and kinetic energy ratios with respect to the gravitational
energy, denoted by ʱ and ʲ , respectively, whose values are here given by

E therm
|

ʱ ≡

| ≈

0 . 3 ,

E grav

(1)

E rot

ʲ ≡

| ≈

0 . 1 .

|

E grav

The sound speed c 0 and the rotational angular velocity ʩ 0 have been calculated in

this paper to fulfill the energy ratios given by Eq. ( 1 ); they are given the following
numerical values

8cms − 1 c 0 ≡ 39956 . ,

(2)

10 − 13 rad ʩ 0 ≡ 8 . 09 × / s .

As is commonly done in papers devoted to simulate binary formation of proto-
stars, we here implement a mass perturbation m i on every particle of mass m 0
according to

m i = m 0 + m 0 a cos ( m ˆ i ) , (3)

where the perturbation amplitude is set to a = 0 . 1 and the mode is fixed to m = 2.

2, as can be seen in Table 1 ,
where we show the collision models considered in this paper. The collision system
has an average density

The onrushing core radius is given by R 0 / 4, or R 0 /

10 − 18 g

cm 3 ; a fictitious gas sphere having this

ˁ 0 = 9 . 2 × /

10 11 s. It should be noticed that mass density would have a free fall time t ff = 6 . 925 ×

these ˁ 0 and t ff are only used to normalize density and time, both in the forthcoming

plots as well as some results given in Table 1 .
The entries of Table 1 are as follows. The first column shows the label of the mod-
els. The second column is the bullet's radius R c given in terms of the target's radius
R 0 . The third column shows the pre-collision velocity in terms of the core's sound