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Published January 2024 | Published
Journal Article Open

ESPRESSO Observations of Gaia BH1: High-precision Orbital Constraints and no Evidence for an Inner Binary

Creators
Nagarajan, Pranav ORCID icon
El-Badry, Kareem1 ORCID icon
Triaud, Amaury H. M. J. ORCID icon
Baycroft, Thomas A. ORCID icon
Latham, David ORCID icon
Bieryla, Allyson ORCID icon
Buchhave, Lars A. ORCID icon
Rix, Hans-Walter ORCID icon
Quataert, Eliot ORCID icon
Howard, Andrew1 ORCID icon
Isaacson, Howard ORCID icon
Hobson, Melissa J. ORCID icon
  • 1. ROR icon California Institute of Technology

Abstract

Abstract We present high-precision radial velocity observations of Gaia BH1, the nearest known black hole (BH). The system contains a solar-type G star orbiting a massive dark companion, which could be either a single BH or an inner BH + BH binary. A BH + BH binary is expected in some models where Gaia BH1 formed as a hierarchical triple, which is attractive because they avoid many of the difficulties associated with forming the system through isolated binary evolution. Our observations test the inner binary scenario. We have measured 115 precise RVs of the G star, including 40 from ESPRESSO with a precision of 3–5 m s⁻¹, and 75 from other instruments with a typical precision of 30–100 m s⁻¹. Our observations span 2.33 orbits of the G star and are concentrated near a periastron passage, when perturbations due to an inner binary would be largest. The RVs are well-fit by a Keplerian two-body orbit and show no convincing evidence of an inner binary. Using REBOUND simulations of hierarchical triples with a range of inner periods, mass ratios, eccentricities, and orientations, we show that plausible inner binaries with periods P_(inner) ≳ 1.5 days would have produced larger deviations from a Keplerian orbit than observed. Binaries with P_(inner) ≲ 1.5 days are consistent with the data, but these would merge within a Hubble time and would thus imply fine-tuning. We present updated parameters of Gaia BH1's orbit. The RVs yield a spectroscopic mass function f (M_( BH)) = 3.9358 ± 0.0002 M⊙ —about 7000σ above the ∼2.5 M⊙ maximum neutron star mass. Including the inclination constraint from Gaia astrometry, this implies a BH mass of M_(BH) = 9.27 ± 0.10 M⊙.

Copyright and License

© 2024. The Author(s). Published by IOP Publishing Ltd on behalf of the Astronomical Society of the Pacific (ASP). Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

 

Acknowledgement

We thank Toshinori Hayashi, Jim Fuller, and Dave Charbonneau for helpful discussions. P.N. and K.E. were supported in part by NSF grant AST-2307232. A.T. and T.B. are supported by a grant from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (grant agreement No. 803193/BEBOP). H.W.R. acknowledges the European Research Council for support from the ERC Advanced Grant ERC-2021-ADG-101054731.

Facilities

ESPRESSO (VLT) -

Software References

astropy (Astropy Collaboration et al. 2013, 2018), REBOUND (Rein et al. 2023), RadVel (Fulton et al. 2020), emcee (Foreman-Mackey et al. 2013), dynesty (Koposov et al. 2023), LEGWORK (Wagg et al. 2022a)

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Additional details

Identifiers Funding Caltech Custom Metadata
ISSN
1538-3873
National Science Foundation
AST-2307232
European Research Council
803193
European Research Council
101054731
Caltech groups
Astronomy Department
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Keywords

  • Space and Planetary Science
  • Astronomy and Astrophysics

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DOI Badge
10.1088/1538-3873/ad1ba7
DOI Badge

DOI

10.1088/1538-3873/ad1ba7

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Resource type
Journal Article
Publisher
IOP Publishing
Published in
Publications of the Astronomical Society of the Pacific, 136(1), 014202, ISSN: 0004-6280.
Languages
English

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  • Creative Commons Attribution 4.0 International
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Created:
February 5, 2024
Modified:
February 5, 2024
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