Massive Star Cluster Formation with Binaries. I. Evolution of Binary Populations

arXiv (Cornell University)

Abstract

We study the evolution of populations of binary stars within massive cluster-forming regions. We simulate the formation of young massive star clusters within giant molecular clouds with masses ranging from 2 x 10$^{4}$ to 3.2 x 10$^{5}$ M$_{\odot}$. We use Torch, which couples stellar dynamics, magnetohydrodynamics, star and binary formation, stellar evolution, and stellar feedback through the AMUSE framework. We find that the binary fraction decreases during cluster formation at all molecular cloud masses. The binaries' orbital properties also change, with stronger and quicker changes in denser, more massive clouds. Most of the changes we see can be attributed to the disruption of binaries wider than 100 au, although the close binary fraction also decreases in the densest cluster-forming region. The binary fraction for O stars remains above 90%, but exchanges and dynamical hardening are ubiquitous, indicating that O stars undergo frequent few-body interactions early during the cluster formation process. Changes to the populations of binaries are a by-product of hierarchical cluster assembly: most changes to the binary population take place when the star formation rate is high and there are frequent mergers between sub-clusters in the cluster-forming region. A universal primordial binary distribution based on observed inner companions in the Galactic field is consistent with the binary populations of young clusters with resolved stellar populations, and the scatter between clusters of similar masses could be explained by differences in their formation history.

Authors 9

1. Claude Cournoyer-Cloutier
2. Alison Sills

   McMaster University

   Affiliation as printed

   Department of Physics and Astronomy , McMaster University , 1280 Main Street West , Hamilton , ON , L8S 4M1 , Canada

3. Brooke Polak

   American Museum of Natural History · Heidelberg University

   Affiliation as printed

   Department of Astrophysics , American Museum of Natural History , 200 Central Park West , New York , NY 10024-5102 , USA

   Zentrum für Astronomie , Institut für Theoretische Astrophysik , Universität Heidelberg , Albert-Ueberle-Str. 2 , 69120 Heidelberg , Germany

4. Steven Rieder

   University of Amsterdam · KU Leuven

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy , University of Amsterdam , Science Park 904 , 1098 XH Amsterdam , The Netherlands

   Institute of Astronomy , Department of Phyiscs and Astronomy , KU Leuven , Celestijnenlaan 200D bus 2401 , 3001 Leuven , Belgium

5. Eric P. Andersson

   American Museum of Natural History

   Affiliation as printed

   Department of Astrophysics , American Museum of Natural History , 200 Central Park West , New York , NY 10024-5102 , USA

6. Sabrina M. Appel

   Rutgers, The State University of New Jersey · American Museum of Natural History

   Affiliation as printed

   Department of Astrophysics , American Museum of Natural History , 200 Central Park West , New York , NY 10024-5102 , USA

   Department of Physics and Astronomy , Rutgers University , 136 Frelinghuysen Road , Piscataway , NJ 08854-8019 , USA

7. Mordecai‐Mark Mac Low
8. Stephen L. W. McMillan

   Drexel University

   Affiliation as printed

   Department of Physics , Drexel University , 3141 Chestnut Street , Philadelphia , PA 19104 , USA

9. Simon Portegies Zwart Aachen Sterrewacht Leiden

   Leiden University · Leiden Observatory

   Affiliation as printed

   Sterrewacht Leiden , Leiden University , Einsteinweg 55 , 2333CC Leiden , The Netherlands