A Tale of Two Circularization Periods

We reanalyze the exquisite eclipsing binary data from the Kepler and TESS missions, focusing on eccentricity measurements at short orbital periods to empirically constrain tidal circularization. We calculate a circularization period of ∼6 days due to nearly circular binaries with long orbital periods ("cold core") but find many binaries with moderate eccentricities that circularize interior to only ∼3 days ("eccentricity envelope"). We show that these features are present in previous spectroscopic surveys. We also reaffirm the statistically significant difference between the eccentricity distributions of young (<1 Gyr) and old (>3 Gyr) binaries. Our work introduces new methods that have the potential to reconcile theoretical predictions with observations to empirically constrain tidal circularization.