The Formation of a 70 M ? Black Hole at High Metallicity

Hirschi

Abstract

A 70 black hole (BH) was discovered in the Milky Way disk in a long-period detached binary system (LB-1) with a high-metallicity 8 B star companion. Current consensus on the formation of BHs from high-metallicity stars limits the BH mass to be below 20 due to strong mass loss in stellar winds. Using analytic evolutionary formulae, we show that the formation of a 70 BH in a high-metallicity environment is possible if wind mass-loss rates are reduced by factor of five. As observations indicate, a fraction of massive stars have surface magnetic fields that may quench the wind mass-loss, independently of stellar mass and metallicity. We confirm such a scenario with detailed stellar evolution models. A nonrotating 85 star model at Z = 0.014 with decreased winds ends up as a 71 star prior to core collapse with a 32 He core and a 28 CO core. Such a star avoids the pair-instability pulsation supernova mass loss that severely limits BH mass and may form a ~70 BH in the direct collapse. Stars that can form 70 BHs at high Z expand to significant sizes, with radii of R ? 600 , however, exceeding the size of the LB-1 orbit. Therefore, we can explain the formation of BHs up to 70 at high metallicity and this result is valid whether or not LB-1 hosts a massive BH. However, if LB-1 hosts a massive BH we are unable to explain how such a binary star system could have formed without invoking some exotic scenarios.}

Citation

Hirschi. (2020). The Formation of a 70 M ? Black Hole at High Metallicity. Astrophysical Journal, 113 -113. https://doi.org/10.3847/1538-4357/ab6d77

• Acceptance Date: Jan 15, 2020
• Publication Date: Feb 20, 2020
• Journal: The Astrophysical Journal
• Print ISSN: 0004-637X
• Publisher: American Astronomical Society
• Pages: 113 -113
• DOI: https://doi.org/10.3847/1538-4357/ab6d77
• Keywords: black hole physics, classical black holes, binary stars
• Publisher URL: https://doi.org/10.3847/1538-4357/ab6d77