The impact of massive stars and black holes on the fate of open star clusters and their tidal streams

TL;DR

This study uses detailed N-body simulations to show how massive OB stars and black holes significantly influence the long-term evolution and observable properties of open star clusters and their tidal streams, highlighting the importance of tidal tail analysis.

Contribution

It demonstrates the critical impact of OB stars and black holes on cluster evolution and introduces a method to use Gaia tidal tail observations to constrain initial cluster conditions.

Findings

OB stars and black holes alter cluster evolution paths.

Initial cluster mass and radius are ambiguous without OB star content.

Tidal tail stellar counts can help determine initial conditions.

Abstract

Context: To investigate how the content of massive OB stars affects the long-term evolution of young open clusters and their tidal streams, and how such an effect influences the constraint of initial conditions by looking at the present-day observations. Aims: OB stars are typically in binaries, have a strong wind mass loss during the first few Myr, and many become black holes. These affect the dynamical evolution of an open star cluster and impact its dissolution in a given Galactic potential. We investigate the correlation between the mass of OB stars and the observational properties of open clusters. Hyades-like star clusters are well represented in the Solar neighborhood and thus allow comparisons with observational data. Methods: We perform a large number of star-by-star numerical $N$-body simulations of Hyades-like star clusters by using the high-performance $N$-body code \textsc{petar} combined with \textsc{galpy}. We also developed the tool to transfer the simulation data to mock observations of Gaia. Results: We find that OB stars and black holes have a major effect on star cluster evolution. Star clusters with the same initial conditions, but a different initial content of OB stars, follow very different evolutionary paths. Thus, the initial total mass and radius of an observed star cluster cannot be unambiguously determined unless the initial content of OB stars is known. We show that the stellar counts in the corresponding tidal tails, that can be identified in the Gaia data, help to resolve this issues. We thus emphasise the importance of exploring not only star-clusters, but also their corresponding tidal tails. These findings are relevant for studies of the formation of massive stars.