Properties of OB star−black hole systems derived from detailed binary evolution models

¹ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
e-mail: nlanger@astro.uni-bonn.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Institute of Astrophysics, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
⁴ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA
⁵ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofisica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
⁷ Center for Astrophysics, Harvard-Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Anton Pannenkoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
⁹ Departamento de Física, Universidade do Estado do Rio Grande do Norte, Mossoró, RN, Brazil
¹⁰ Departamento de Física, Universidade Federal do Rio Grande do Norte, UFRN, CP 1641, Natal, RN 59072-970, Brazil
¹¹ Department of Physics and Astronomy, Hicks Building, Hounsfield Road, University of Sheffield, Sheffield S3 7RH, UK
¹² AIP Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
¹³ School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
¹⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
¹⁵ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
¹⁶ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
¹⁷ Universidad de La Laguna, Dpto. Astrofisica, 38206 La Laguna, Tenerife, Spain
¹⁸ LMU Munich, Universitätssternwarte, Scheinerstrasse 1, 81679 München, Germany
¹⁹ Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, USA
²⁰ Armagh Observatory, College Hill, Armagh BT61 9DG, UK
²¹ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
²² Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg, Germany
²³ Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Hoegh-Guldbergs Gade 6B, 8000 Aarhus C, Denmark
²⁴ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
²⁵ IAASARS, National Observatory of Athens, Vas. Pavlou and I. Metaxa, Penteli 15236, Greece

Received: 20 December 2019
Accepted: 9 April 2020

Abstract

Context. The recent gravitational wave measurements have demonstrated the existence of stellar mass black hole binaries. It is essential for our understanding of massive star evolution to identify the contribution of binary evolution to the formation of double black holes.

Aims. A promising way to progress is investigating the progenitors of double black hole systems and comparing predictions with local massive star samples, such as the population in 30 Doradus in the Large Magellanic Cloud (LMC).

Methods. With this purpose in mind, we analysed a large grid of detailed binary evolution models at LMC metallicity with initial primary masses between 10 and 40 M_⊙, and identified the model systems that potentially evolve into a binary consisting of a black hole and a massive main-sequence star. We then derived the observable properties of such systems, as well as peculiarities of the OB star component.

Results. We find that ∼3% of the LMC late-O and early-B stars in binaries are expected to possess a black hole companion when stars with a final helium core mass above 6.6 M_⊙ are assumed to form black holes. While the vast majority of them may be X-ray quiet, our models suggest that these black holes may be identified in spectroscopic binaries, either by large amplitude radial velocity variations (≳50 km s⁻¹) and simultaneous nitrogen surface enrichment, or through a moderate radial velocity (≳10 km s⁻¹) and simultaneous rapid rotation of the OB star. The predicted mass ratios are such that main-sequence companions can be excluded in most cases. A comparison to the observed OB+WR binaries in the LMC, Be and X-ray binaries, and known massive black hole binaries supports our conclusion.

Conclusions. We expect spectroscopic observations to be able to test key assumptions in our models, with important implications for massive star evolution in general and for the formation of double black hole mergers in particular.