Dynamical Evolution of White Dwarf Triples in the Era of Gaia

The Gaia mission aims to measure the position and distance of more than a billion stars with unprecedented precision. The recent Gaia data release has uncovered various puzzles, with our particular interest regarding White Dwarfs (WDs)–the end result of sun-like star evolution. Gaia has detected many WDs in binary and triple configurations, and while observations suggest that triple stellar systems are common in our Galaxy, not much attention was devoted to WDs in triples. For stability reasons, these triples must have hierarchical configurations, i.e., two stars are on a tight orbit (the inner binary), with the third companion on a wider orbit about the inner binary. In such a system, the two orbits torque each other via the eccentric Kozai-Lidov mechanism, which can alter the orbital configuration of the inner binary. We simulate thousands of triple stellar systems for over 10 Gyr, tracking gravitational interactions, tides, general relativity, and stellar evolution up to their WD fate. As we will show, three-body dynamics coupled with stellar evolution is a critical channel for forming tight WD binaries or merging a WD binary. The simulated systems are then compared to observed WD triples from Gaia. We find that including the effect of kicks from WD formation is crucial for producing a distribution of the inner binary-tertiary separations that is consistent with Gaia observations. Lastly, we leverage this consistency to estimate that, as a lower limit, 30% of solar-type stars in the local 200 parsecs were born in triples.