Recent Advances in Binary Star Formation Using SPH

The Smoothed Particle Hydrodynamics (SPH) numerical method was introduced by Lucy [20] and Gingold and Monaghan [21]. Its first application was in the field of star formation, where it was used to study whether or not a rapidly-rotating polytrope could undergo fission to form a close binary system [20, 22]. Since this initial application, SPH has been widely used in the study of star formation, for example [23, 31, 29, 17, 35, 10, 7, 25, 34, 2, 28, 33, 39, 16]. SPH is has many attributes which make it particularly well suited to the study of star formation. SPH is Lagrangian and does not require a computational grid. Thus, it can efficiently follow problems with large density contrasts since computational effort is not wasted simulating the low-density regions. Also, recent SPH implementations [19, 26, 9, 32] use spatially and temporally varying smoothing lengths so that the resolution increases automatically with increasing density; the complex multi-grid and adaptive-grid schemes that are used for finite difference methods are avoided. In this proceedings, we review some of the recent advances in the study of binary star formation that have been made using SPH. In Section 2, we discuss the importance of always resolving the Jeans mass in numerical studies of self-gravitating gas. While this has been demonstrated using various types of hydrodynamic code, we concentrate specifically on the problems that can arise if this criterion is not obeyed with SPH. In Section 3, we demonstrate that, for the first time, it is now possible to perform three-dimensional hydrodynamic calculations which follow the collapse of a molecular cloud core to stellar densities. These calculations are performed with SPH. Finally, in Section 4, we discuss how SPH has been used to study the evolution of a protobinary system as it accretes from an infalling gaseous envelope and how this work can lead to predictions of the properties of binary stars.