Comparison of Static and Evolving Potentials in the Orbital Dynamics of Globular Clusters in the Central Region of the Galaxy
Anisa Bajkova, Anton Smirnov, Vadim Bobylev
TL;DR
This paper investigates how static versus evolving Galactic potentials, including a rotating central bar, influence the regular vs chaotic orbital dynamics of globular clusters in the Galaxy’s inner $3.5$ kpc. Using $6$D phase-space data from Gaia EDR3 and refined distances, the authors compare axisymmetric and barred potentials under both static and semi-cosmological evolving models, diagnosing chaos with a frequency-drift method that uses a long integration time of $120$ Gyr and a threshold of $\lg(\Delta f_i)_t = -2.24$. They find only modest differences when moving from static to evolving potentials ($r \approx 0.84$ correlation), while the central bar has a more pronounced effect on chaos, with a handful of clusters changing class between configurations; the evolving-bar case yields $28$ regular and $17$ chaotic clusters. The results support the idea that simultaneous evolution of mass and size components partly counteracts chaos-inducing effects in the central regions, while bar-driven dynamics remain a key driver of orbital chaos for GCs near the Galactic center, providing insights into GC survival and orbital structure in realistic time-varying potentials.
Abstract
A comparative analysis of the dynamics of the orbital motion (regular or chaotic) of 45 globular clusters in the central region of the Galaxy with a radius of 3.5 kpc is carried out. The static and evolving (based on the semi-analytical cosmological model of Gomez et al. (2010) and Hagi et al. (2015)) potentials of the Galaxy are considered both in the form of an axisymmetric and non-axisymmetric potential of the Galaxy with a rotating elongated bar with the following parameters at the present time: mass $10^{10} M_\odot$, length of the major semi-axis 5 kpc, rotation angle of the bar axis 25$^o$, angular velocity of rotation 40 km s$^{-1}$ kpc$^{-1}$ . To form the 6D-phase space required for integrating the orbits, the most accurate astrometric data to date from the Gaia satellite (Vasiliev \& Baumgardt, 2021), as well as new refined average distances (Baumgardt \& Vasiliev, 2021) were used. We used a frequency method for analysis of the chaotic/regular orbital motion of all 45 GCs. The results are summarized in the table, which provides an overview of each GC in our sample, the degree of chaotization in both the static and evolving potentials, and the influence of the central rotating bar on the degree of orbital chaotization in both cases. It is shown that the orbital dynamics have undergone minor changes during the transition from the static to the evolving potential. This confirms our previously obtained result that changes in the masses and sizes of the gravitational potential components act on orbital parameters in opposite ways, and at small galactocentric distances this influence is maximally compensated, while the orbits of distant objects and objects with large apocentric distances experience the greatest influence.