Dynamics of tidally captured planets in the Galactic Center

TL;DR

This study uses high-accuracy simulations to explore how planets near the Galactic Center can be tidally captured by the supermassive black hole, revealing their orbital characteristics and potential observability.

Contribution

It provides new insights into the dynamics of tidally captured planets and predicts their orbital properties based on initial conditions and simple analytic models.

Findings

Tidally captured planets stay close to their parent star's orbit.

Prograde captured planets have predictable semi-major axes.

Planets initially bound to S-stars are captured on highly eccentric orbits.

Abstract

Recent observations suggest ongoing planet formation in the innermost parsec of the Galactic center (GC). The super-massive black hole (SMBH) might strip planets or planetary embryos from their parent star, bringing them close enough to be tidally disrupted. Photoevaporation by the ultraviolet field of young stars, combined with ongoing tidal disruption, could enhance the near-infrared luminosity of such starless planets, making their detection possible even with current facilities. In this paper, we investigate the chance of planet tidal captures by means of high-accuracy N-body simulations exploiting Mikkola's algorithmic regularization. We consider both planets lying in the clockwise (CW) disk and planets initially bound to the S-stars. We show that tidally captured planets remain on orbits close to those of their parent star. Moreover, the semi-major axis of the planet orbit can be predicted by simple analytic assumptions in the case of prograde orbits. We find that starless planets that were initially bound to CW disk stars have mild eccentricities and tend to remain in the CW disk. However, we speculate that angular momentum diffusion and scattering with other young stars in the CW disk might bring starless planets on low-angular momentum orbits. In contrast, planets initially bound to S-stars are captured by the SMBH on highly eccentric orbits, matching the orbital properties of the G1 and G2 clouds. Our predictions apply not only to planets but also to low-mass stars initially bound to the S-stars and tidally captured by the SMBH.