A Trojan Horse for White Dwarfs: Evolution of co-orbital asteroids under post-main sequence mass loss and radiative effects

Many white dwarfs exhibit spectral signatures of metal pollution in their atmospheres. Without continuous replenishment, though, these metals should sink inward and become unobservable within several millions of years. The surfaces of these polluted white dwarfs must therefore possess disks of rocky debris residing within about 1 Solar radius, acting as an ongoing source of material; however, these disks would be too close-in to survive the stars’ red giant branch phases, during which the star swells to ~1 AU, so they must arise just at the onset of the white dwarf phase. The source of this rocky debris and the mechanism by which it reaches the stellar surface at the start of the white dwarf phase are both unknown. Several efforts over the past decade have showed that stellar mass-loss and increased radiative effects during the post-main sequence can cause significant orbital evolution of small bodies in the stellar system, highlighting that asteroids in rings at various distances from the host star can be made to fall in towards the star during the appropriate timeframe. While promising, these works have not considered all possible sources of debris disk material. Few works have studied the eventual fate of Trojan asteroids, those bodies residing in co-orbital configurations with giant planets—in the Solar System, Jupiter has thousands of Trojan asteroids librating around its stable Lagrange points. We would expect Jupiter-analogues in other planetary systems to possess a similarly numerous repository of Trojan asteroids, giving us an extensive population of rocky bodies that may contribute to white dwarf pollution if they can be freed from their co-orbital configuration. In this talk, we describe how gravitational and radiative effects during the post-main sequence can do just that, causing previously-stable, co-orbital asteroids to fall in towards the white dwarf. Using N-body simulations, we delineate the regime of asteroid spins and sizes within which the Yarkovsky effect can drive Trojan asteroids out of the Lagrange point, indicating that they may contribute to white dwarf pollution.