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A Sun-like star orbiting a black hole

El-Badry, Kareem and Rix, Hans-Walter and Quataert, Eliot and Howard, Andrew W. and Isaacson, Howard and Fuller, Jim and Hawkins, Keith and Breivik, Katelyn and Wong, Kaze W. K. and Rodriguez, Antonio C. and Conroy, Charlie and Shahaf, Sahar and Mazeh, Tsevi and Arenou, Frédéric and Burdge, Kevin B. and Bashi, Dolev and Faigler, Simchon and Weisz, Daniel R. and Seeburger, Rhys and Almada Monter, Silvia and Wojno, Jennifer (2023) A Sun-like star orbiting a black hole. Monthly Notices of the Royal Astronomical Society, 518 (1). pp. 1057-1085. ISSN 0035-8711. doi:10.1093/mnras/stac3140.

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We report discovery of a bright, nearby (⁠G = 13.8; d = 480 pc⁠) Sun-like star orbiting a dark object. We identified the system as a black hole candidate via its astrometric orbital solution from the Gaia mission. Radial velocities validated and refined the Gaia solution, and spectroscopy ruled out significant light contributions from another star. Joint modelling of radial velocities and astrometry constrains the companion mass of M₂ = 9.62 ± 0.18 M_⊙⁠. The spectroscopic orbit alone sets a minimum companion mass of M₂ > 5 M_⊙⁠; if the companion were a 5 M_⊙ star, it would be 500 times more luminous than the entire system. These constraints are insensitive to the mass of the luminous star, which appears as a slowly rotating G dwarf (⁠T_(eff) = 5850 K⁠, log g = 4.5, M = 0.93 M_⊙⁠), with near-solar metallicity (⁠[Fe/H] = −0.2⁠) and an unremarkable abundance pattern. We find no plausible astrophysical scenario that can explain the orbit and does not involve a black hole. The orbital period, P_(orb) = 185.6 d, is longer than that of any known stellar-mass black hole binary. The system’s modest eccentricity (e = 0.45), high metallicity, and thin-disc Galactic orbit suggest that it was born in the Milky Way disc with at most a weak natal kick. How the system formed is uncertain. Common envelope evolution can only produce the system’s wide orbit under extreme and likely unphysical assumptions. Formation models involving triples or dynamical assembly in an open cluster may be more promising. This is the nearest known black hole by a factor of 3, and its discovery suggests the existence of a sizable population of dormant black holes in binaries. Future Gaia releases will likely facilitate the discovery of dozens more.

Item Type:Article
Related URLs:
URLURL TypeDescription
El-Badry, Kareem0000-0002-6871-1752
Rix, Hans-Walter0000-0003-4996-9069
Quataert, Eliot0000-0001-9185-5044
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Fuller, Jim0000-0002-4544-0750
Hawkins, Keith0000-0002-1423-2174
Breivik, Katelyn0000-0001-5228-6598
Wong, Kaze W. K.0000-0001-8432-7788
Rodriguez, Antonio C.0000-0003-4189-9668
Conroy, Charlie0000-0002-1590-8551
Shahaf, Sahar0000-0001-9298-8068
Mazeh, Tsevi0000-0002-3569-3391
Arenou, Frédéric0000-0003-2837-3899
Burdge, Kevin B.0000-0002-7226-836X
Bashi, Dolev0000-0002-9035-2645
Faigler, Simchon0000-0002-8368-5724
Weisz, Daniel R.0000-0002-6442-6030
Seeburger, Rhys0000-0001-8898-9463
Almada Monter, Silvia0000-0003-4977-5897
Wojno, Jennifer0000-0002-3233-3032
Additional Information:© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( We thank Morgan Macleod, E. Sterl Phinney, Rohan Naidu, Lieke van Son, Mathieu Renzo, and Tom Maccarone for helpful discussions, and Vedant Chandra for help with data reduction. We are grateful to Yuri Beletsky, Sam Kim, Angela Hempel, and Régis Lachaume for observing help. HWR acknowledges the European Research Council for the ERC Advanced Grant [101054731]. This research made use of pystrometry, an open source python package for astrometry time-series analysis (Sahlmann 2019). This work made use of astropy,6 a community-developed core python package and an ecosystem of tools and resources for astronomy (Astropy Collaboration 2022). This project was developed in part at the Gaia Fête, held at the Flatiron Institute’s Center for Computational Astrophysics in June 2022, and in part at the Gaia Hike, held at the University of British Columbia in June 2022. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Based on observations obtained at the international Gemini Observatory, a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). DATA AVAILABILITY. Data used in this study are available upon request from the corresponding author.
Group:Astronomy Department
Funding AgencyGrant Number
European Research Council (ERC)101054731
Gaia Multilateral AgreementUNSPECIFIED
Gemini PartnershipUNSPECIFIED
Issue or Number:1
Record Number:CaltechAUTHORS:20230105-896211000.63
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118736
Deposited By: George Porter
Deposited On:06 Jan 2023 15:57
Last Modified:06 Jan 2023 15:57

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