"Evolving orbits in planetary and stellar systems"
Secular gravitational interactions in hierarchical systems such as multiple star systems with or without planets can accelerate the tidal shrinkage of stellar and planetary orbits due to the excitation of high eccentricities. This process, also known as high-eccentricity migration, has been proposed to explain the origin of hot Jupiters (HJs) in stellar binaries, and of short-period binaries in stellar triples. Here, we revisit this scenario in several contexts with more complex hierarchies, using an efficient algorithm to model the secular dynamics. First, we consider a number of alternative high-eccentricity migration scenarios for forming hot Jupiters in stellar binaries with multiple planets, and in stellar triple systems. Study of such alternative scenarios is important given the low formation efficiency of HJs in stellar binaries in traditional scenarios. Second, we consider the evolution of stellar quadruple systems, in both the 2+2 (two binaries orbiting each other’s barycentre) and 3+1 (triple orbited by a fourth star) configurations. We show that secular evolution during the main sequence can lead to tidal shrinkage of the inner orbit(s), and which is roughly consistent with observations. Alternatively, if tidal shrinkage is avoided during the main sequence, then dynamical and stellar evolution can also ultimately lead to the collision of two white dwarfs. Such collisions are likely to result in a Type Ia supernova (SNe Ia) explosion. We show that the collision-induced SNe Ia rates from quadruples are comparable to those previously considered in stellar triples. However, the rates are several orders of magnitude lower compared to the observations, indicating that collision-induced SNe Ia from triples and quadruples are rare.