Second-generation planet formation after tidal disruption from common envelope evolution

TL;DR

This paper proposes a new second-generation planet formation mechanism around white dwarfs, where a tidally disrupted stellar companion forms a gas giant from an accretion disc, explaining planets like WD 1856+534 b.

Contribution

It introduces a novel formation channel for planets around white dwarfs via tidal disruption and disc gravitational instability, supported by stellar evolution models.

Findings

Disrupted companions above 0.15 solar masses can form unstable discs

WD 1856+534 b may have formed near its current orbit

This mechanism offers an alternative to planetary migration scenarios

Abstract

We propose that certain white dwarf (WD) planets, such as WD 1856+534 b, may form out of material from a stellar companion that tidally disrupts from common envelope evolution with the WD progenitor star. The disrupted companion shreds into an accretion disc, out of which a gas giant protoplanet forms due to gravitational instability. To explore this scenario, we make use of detailed stellar evolution models consistent with WD 1856+534. The minimum mass companion that produces a gravitationally-unstable disc after tidal disruption is $\sim0.15\,\mathrm{M}_\odot$. In this scenario, WD 1856+534 b might have formed at or close to its present separation, in contrast to other proposed scenarios where it would have migrated in from a much larger separation. Planet formation from tidal disruption is a new channel for producing second-generation planets around WDs.