Star formation at the Galactic Centre: coevolution of multiple young stellar discs

Abstract

Studies of the Galactic Centre suggest that in-situ star formation may have given rise to the observed stellar population near the central supermassive black hole (SMBH). Direct evidence for a recent starburst is provided by the currently observed young stellar disc (2-7 Myr) in the central 0.5 pc of the Galaxy. This result suggests that star formation in galactic nuclei may occur close to the SMBH and produce initially flattened stellar discs. Here we explore the possible build-up and evolution of nuclear stellar clusters near SMBHs through in-situ star formation producing stellar discs similar to those observed in the Galactic Centre and other nuclei. We make use of N-body simulations to model the evolution of multiple young stellar discs, and explore the potential observable signatures imprinted by such processes. Each of the five simulated discs is evolved for 100 Myr before the next one is introduced in the system. We find that populations born at different epochs show different morphologies and kinematics. Older and presumably more metal poor populations are more relaxed and extended, while younger populations show a larger amount of rotation and flattening. We conclude that star formation in central discs can reproduce the observed properties of multiple stellar populations in galactic nuclei differing in age, metallicity and kinematic properties.

A Deep View into the Nucleus of the Sagittarius Dwarf Spheroidal Galaxy with MUSE. II. Kinematic Characterization of the Stellar Populations

“…We will discuss this in the next section. From N-body simulations, Mastrobuono-Battisti & Perets (2013, 2016; Mastrobuono-Battisti et al (2019b) found that the young structures can survive despite being embedded in an older population. Moreover, they are found to rotate faster than the population in which they are embedded.…”

Kinematic Structure of the Galactic Center S-cluster

“…The population of S-stars consisting of 2 disks is not relaxed, hence any current configuration is subject to resonant and non-resonant relaxation processes in the nuclear star cluster. The configuration of 2 perpendicular stellar disks can be stable over a timescale of 10 8 years as demonstrated in the simulations by Mastrobuono-Battisti et al (2019) that we refer to later. In the current section we mention key dynamical processes that might have contributed to the X-structure and so far could have influenced it.…”

“…The possibility of different coexisting stellar disks in the Galactic Center has also been discussed theoretically by Mastrobuono-Battisti et al (2019). Here, the authors simulate multiple stellar disks in the central stellar cluster.…”

Cool stars in the Galactic center as seen by APOGEE

“…Tsatsi et al 2017showed that using N-body simulation of inspiralling clusters to the center of the Milky Way can reproduce both the morphological and kinematical properties of the NSC. On the other hand, Mastrobuono-Battisti et al (2019) showed that in the presence of an aspherical, time-variable potential (e.g., due to the presence of a discrete stellar black hole cusp), counter-rotating disks can perturb the dynamics of older stellar populations leading to accelerated relaxation, while the younger populations show a larger amount of rotation. Younger populations always show larger rotation compared to older ones, but the difference is even larger for counter-rotating disks.…”