Can Gaia find planets around white dwarfs?

The Gaia spacecraft presents an unprecedented opportunity to reveal the population of long period (a > 1 au) exoplanets orbiting stars across the H-R diagram, including white dwarfs. White dwarf planetary systems have played an important role in the study of planetary compositions, from their unique ability to provide bulk elemental abundances of planetary material in their atmospheres. Yet, very little is known about the population of planets around white dwarfs. This paper predicts the population of planets that Gaia will detect around white dwarfs, evolved from known planets orbiting main-sequence stars. We predict that Gaia will detect 8 ± 2 planets around white dwarfs: $8\pm \, 3{{\ \rm per\ cent}}$ will lie inside 3 au and $40\pm 10\, {{\ \rm per\ cent}}$ will be less massive than Jupiter. As surviving planets likely become dynamically detached from their outer systems, those white dwarfs with Gaia detected planets may not have planetary material in their atmospheres. Comparison between the predicted planet population and that found by Gaia will reveal the importance of dynamical instabilities and scattering of planets after the main-sequence, as well as whether photoevaporation removes the envelopes of gas giants during their giant branch evolution.