Fragmentation of elongated cylindrical clouds. III - Formation of binary and multiple systems

Abstract

Using three-dimensional hydrodynamical simulations, the fragmentation of uniform, isothermal, elongated molecular clouds, slowly rotating around an axis perpendicular to their elongation is studied. It is argued that this process could result in the formation of binary and multiple stars. This new method for forming binary stars can explain wide binaries with large eccentricities and various mass ratios. At relatively low initial Jeans numbers (the ratio of the absolute value of gravitational to thermal energies), a simple binary system is formed. For higher initial Jeans numbers, multiple fragmentation occurs between the binary fragments, forming a multiple system. This spontaneous additional fragmentation is believed to be induced by rotation. The disks around the fragments were observed to be perturbed by the presence of multiple fragments resulting in a m = 1 disk instability. This instability results in the formation of another companion.