White Dwarf Planetary Systems Research Articles

Liberating exomoons in white dwarf planetary systems

Previous studies indicate that more than a quarter of all white dwarf (WD) atmospheres are polluted by remnant planetary material, with some WDs being observed to accrete the mass of Pluto in 10^6 years. The short sinking timescale for the pollutants indicate that the material must be frequently replenished. Moons may contribute decisively to this pollution process if they are liberated from their parent planets during the post-main-sequence evolution of the planetary systems. Here, we demonstrate that gravitational scattering events among planets in WD systems easily triggers moon ejection. Repeated close encounters within tenths of a planetary Hill radii are highly destructive to even the most massive, close-in moons. Consequently, scattering increases both the frequency of perturbing agents in WD systems, as well as the available mass of polluting material in those systems, thereby enhancing opportunities for collision and fragmentation and providing more dynamical pathways for smaller bodies to reach the WD. Moreover, during intense scattering, planets themselves have pericenters with respect to the WD of only a fraction of an AU, causing extreme Hill-sphere contraction, and the liberation of moons into WD-grazing orbits. Many of our results are directly applicable to exomoons orbiting planets around main sequence stars.

Magnetic interaction in ultra-compact binary systems

This article reviews the current works on ultra-compact double-degenerate binaries in the presence of magnetic interaction, in particular, unipolar induction. The orbital dynamics and evolution of compact white-dwarf pairs are discussed in detail. Models and predictions of electron cyclotron masers from unipolar-inductor compact binaries and unipolar-inductor white-dwarf planetary systems are presented. Einstein–Laub effects in compact binaries are briefly discussed.

Electron-cyclotron maser emission from white dwarf pairs and white dwarf planetary systems

By analogy to Jovian radio emissions powered by the electromagnetic interaction between Jupiter and its moons, we propose that close magnetic-nonmagnetic white-dwarf pairs and white-dwarf planetary systems are strong radio sources. A simple model is developed to predict the flux densities of radio emission generated by a loss-cone-driven electron-cyclotron maser. The radio emission from these systems has high brightness temperatures, is highly polarized, and varies on a periodic cycle following the orbital rotation. Masers from magnetic-nonmagnetic white-dwarf pairs, with orbital periods <10 min, are expected to be detectable over a wide range of radio frequencies. Terrestrial planets in close orbits about magnetic white dwarfs, with orbital periods $\la 30$ hr, can also produce detectable radio emission, thus providing a means to identify Earth-sized extrasolar planets.