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

¹ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
e-mail: long.wang@astron.s.u-tokyo.ac.jp
² RIKEN Center for Computational Science, 7-1-26 Minatojima-minami-machi, Chuo-ku, Kobe, Hyogo 648-0047, Japan
³ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
e-mail: tereza.jerabkova@es.int

Received: 21 July 2021
Accepted: 8 September 2021

Abstract

Context. We use present-day observations 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.

Aims. OB stars are typically found in binaries. They have a strong wind mass loss during the first few million years 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 using the high-performance N-body code PETAR combined with GALPY.

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, which can be identified in the Gaia data, help to resolve this issues. We thus emphasize 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.