A new insight into the Galactic potential: A simple secular model for the evolution of binary systems in the solar neighbourhood

Abstract

Context. Among the main effects that the Milky Way exerts in binary systems, the Galactic tide is the only one that is not probabilistic and can be deduced from a potential. Therefore, it is possible to perform an analysis of the global structure of the phase space of binary systems in the solar neighbourhood using the Galactic potential. Aims. The aim of this work is to obtain a simple model to study the collisionless dynamical evolution of generic wide binaries systems in the solar neighbourhood. Methods. Through an averaging process, we reduced the three-dimensional potential of the Galaxy to a secular one-degree of freedom model. The accuracy of this model was tested by comparing its predictions with numerical simulations of the exact equations of motion of a two-body problem disturbed by the Galaxy.Results. Using the one-degree of freedom model, we developed a detailed dynamical study, finding that the secular Galactic tide period changes as a function of the separation of the pair, which also gives a dynamical explanation for the arbitrary classification between "wide" and "tight" binaries. Moreover, the secular phase space for a generic gravitationally bound pair is similar to the dynamical structure of a Lidov-Kozai resonance, but surprisingly this structure is independent of the masses and semimajor axis of the binary system. Thus, the Galactic potential is able to excite the initially circular orbit of binary systems to high values of eccentricity, which has important implications for studies of binary star systems (with and without exoplanets), comets, and Oort cloud objects.

Secular dynamics of binaries in stellar clusters – I. General formulation and dependence on cluster potential

“…It is important that the orbital elements are defined with respect to a reference frame with axis directions fixed in time (cf. Brasser 2001;Veras & Evans 2013a;Correa-Otto et al 2017). In the limit of the cluster tide going to zero these orbital elements stay constant.…”

Chaotic dynamics of wide triples induced by galactic tides: a novel channel for producing compact binaries, mergers, and collisions

“…Here we follow the simplified model of Heisler & Tremaine (1986), taking into account only the leading term of the vertical tide, neglecting perturbations on other directions (which are about ∼ 15 times smaller, Heisler & Tremaine 1986). Various studies looked on the additional terms (e.g Veras & Evans 2013;Correa-Otto et al 2017) and found the behaviour to be qualitatively similar to Heisler & Tremaine (1986).…”

“…Secular evolution of stellar-binaries could also occur due to perturbation by external non-stellar potentials, such as binaries perturbed by a massive black hole in galactic nuclei (Antonini & Perets 2012;Prodan et al 2015); binaries in cluster potentials (Hamilton & Rafikov 2019a, or wide binaries perturbed by the Galactic tidal field (Correa-Otto et al 2017). In fact, already decades ago the secular evolution of Oort cloud objects due to the Galactic tidal field was shown to be important for the production of highly eccentric comets and the formation of long-period and sun-grazing comets (e.g Heisler & Tremaine 1986).…”

First discovery of an ultra-cool white dwarf benchmark in common proper motion with an M dwarf

“…Their wide physical separations mean that they have weak binding energy -the orbits can easily be disrupted, hence they are assumed to be coeval and have evolved independently. A large sample of such binaries can be used to probe the Galactic gravitational potential (Chanamé & Gould 2004;Quinn & Smith 2009;Monroy-Rodríguez & Allen 2014;Correa-Otto et al 2017). CPM systems containing a white dwarf and a burning star provide the advantage that the age of the system can be estimated from white dwarf cooling, while the progenitor chemistry and the radial velocity of the system can be extracted from the co-moving counterpart.…”