A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate

Jayasinghe, T. and Stanek, K. Z. and Thompson, Todd A. and Kochanek, C. S. and Rowan, D. M. and Vallely, P. J. and Strassmeier, K. G. and Weber, M. and Hinkle, J. T. and Hambsch, F. -J. and Martin, D. V. and Prieto, J. L. and Pessi, T. and Huber, D. and Auchettl, K. and Lopez, L. A. and Ilyin, I. and Badenes, C. and Howard, A. W. and Isaacson, H. and Murphy, S. J. (2021) A unicorn in monoceros: the 3 M⊙ dark companion to the bright, nearby red giant V723 Mon is a non-interacting, mass-gap black hole candidate. Monthly Notices of the Royal Astronomical Society, 504 (2). pp. 2577-2602. ISSN 0035-8711

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Abstract

We report the discovery of the closest known black hole candidate as a binary companion to V723 Mon. V723 Mon is a nearby (⁠d∼460pc⁠), bright (V ≃ 8.3 mag), evolved (Teff, giant ≃ 4440 K, and Lgiant ≃ 173 L⊙) red giant in a high mass function, f(M) = 1.72 ± 0.01 M⊙, nearly circular binary (P = 59.9 d, e ≃ 0). V723 Mon is a known variable star, previously classified as an eclipsing binary, but its All-Sky Automated Survey, Kilodegree Extremely Little Telescope, and Transiting Exoplanet Survey Satellite light curves are those of a nearly edge-on ellipsoidal variable. Detailed models of the light curves constrained by the period, radial velocities, and stellar temperature give an inclination of 87.0 ∘+1.7∘ −1.4∘ ⁠, a mass ratio of q ≃ 0.33 ± 0.02, a companion mass of Mcomp = 3.04 ± 0.06 M⊙, a stellar radius of Rgiant = 24.9 ± 0.7 R⊙, and a giant mass of Mgiant = 1.00 ± 0.07 M⊙. We identify a likely non-stellar, diffuse veiling component with contributions in the B and V band of ∼63 per cent and ∼24 per cent⁠, respectively. The SED and the absence of continuum eclipses imply that the companion mass must be dominated by a compact object. We do observe eclipses of the Balmer lines when the dark companion passes behind the giant, but their velocity spreads are low compared to observed accretion discs. The X-ray luminosity of the system is LX≃7.6×1029 ergs s−1⁠, corresponding to L/Ledd ∼ 10−9. The simplest explanation for the massive companion is a single compact object, most likely a black hole in the ‘mass gap’.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: File reproduced in accordance with the copyright policy of the publisher/author.
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Date Deposited: 12 Jul 2022 23:00
Last Modified: 13 Jul 2022 00:14
Uncontrolled Keywords: binaries: spectroscopic; stars: black holes; stars: individual: V723 Mon; Astrophysics - Solar and Stellar Astrophysics; Astrophysics - High Energy Astrophysical Phenomena; General Relativity and Quantum Cosmology
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510109 Stellar astronomy and planetary systems
Socio-Economic Objectives (2020): 28 EXPANDING KNOWLEDGE > 2801 Expanding knowledge > 280120 Expanding knowledge in the physical sciences
Identification Number or DOI: https://doi.org/10.1093/mnras/stab907
URI: http://eprints.usq.edu.au/id/eprint/47892

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