Throwing Icebergs at White Dwarfs

Abstract

White dwarfs have atmospheres that are expected to consist nearly entirely of hydrogen and helium, since heavier elements will sink out of sight on short timescales. However, observations have revealed atmospheric pollution by heavier elements in about a quarter to a half of all white dwarfs. While most of the pollution can be accounted for with asteroidal or dwarf planetary material, recent observations indicate that larger planetary bodies, as well as icy and volatile material from Kuiper belt analog objects, are also viable sources of pollution. The commonly accepted pollution mechanisms, namely scattering interactions between planetary bodies orbiting the white dwarfs, can hardly account for pollution by objects with large masses or long-period orbits.Here we report on a mechanism that naturally leads to the emergence of massive body and icy and volatile material pollution. This mechanism occurs in wide binary stellar systems, where the mass loss of the planets' host stars during post main sequence stellar evolution can trigger the Eccentric Kozai-Lidov mechanism. This mechanism leads to large eccentricity excitations, which can bring massive and long-period objects close enough to the white dwarfs to be accreted. We find that this mechanism readily explains and is consistent with observations.

Formation and Merging of Mass Gap Black Holes in Gravitational-wave Merger Events from Wide Hierarchical Quadruple Systems

“…Since our knowledge of the quadruple frequency is incomplete, it suffices to illustrate that if 0.01-0.1% of all the quadruples fall into our formation channel, they have a chance of reproducing a mass-gap merger event detectable with LIGO. Lastly, we note that we consider it unlikely for the inner binary to merge while the stars are on their main sequence, as mass loss and the subsequent widening of the orbit will make the inner binary more susceptible to LK oscillations (Shappee & Thompson 2012;Stephan, Naoz & Zuckerman 2017).…”

Tidal disruption of planetary bodies by white dwarfs I: a hybrid sph-analytical approach

“…The origin of material at such close proximity to the WD is clearly not primordial (Graham et al 1990), since the WD disruption radius is of the order of the progenitor star's main-sequence physical radius (Bear & Soker 2013). It is instead thought to originate from planetary bodies which are perturbed by some mechanism (Debes & Sigurdsson 2002;Bonsor et al 2011;Debes et al 2012;Shappee & Thompson 2013;Michaely & Perets 2014;Veras & Gänsicke 2015;Stone et al 2015;Hamers & Portegies Zwart 2016;Veras 2016;Payne et al 2016;Caiazzo & Heyl 2017;Payne et al 2017;Petrovich & Muñoz 2017;Stephan et al 2017;Smallwood et al 2018) to highly eccentric orbits with proximity to the WD, and are subsequently tidally disrupted to form a circumstellar disc of planetary debris.…”

The critical binary star separation for a planetary system origin of white dwarf pollution

“…Both Hamers & Portegies Zwart (2016) and Stephan et al (2017) instead considered binary systems with a single other non-coplanar body. The mass of this body was sampled in a distribution that straddles traditional definitions of asteroid and planet (from 0.3 Mars masses to one Jupiter mass in Hamers & Portegies Zwart 2016, and for Eris and Neptune masses in Stephan et al 2017).…”

“…The mass of this body was sampled in a distribution that straddles traditional definitions of asteroid and planet (from 0.3 Mars masses to one Jupiter mass in Hamers & Portegies Zwart 2016, and for Eris and Neptune masses in Stephan et al 2017). They showed that Lidov-Kozai oscillations (which feature oscillations of both eccentricity and inclination) can perturb the third body into the white dwarf, polluting it.…”