Pranav Nagarajan, Kareem El-Badry, Amaury H. M. J. Triaud, Thomas A. Baycroft, David Latham, Allyson Bieryla, Lars A. Buchhave, Hans-Walter Rix, Eliot Quataert, Andrew Howard, Howard Isaacson, Melissa J. Hobson
{"title":"ESPRESSO Observations of Gaia BH1: High-precision Orbital Constraints and no Evidence for an Inner Binary","authors":"Pranav Nagarajan, Kareem El-Badry, Amaury H. M. J. Triaud, Thomas A. Baycroft, David Latham, Allyson Bieryla, Lars A. Buchhave, Hans-Walter Rix, Eliot Quataert, Andrew Howard, Howard Isaacson, Melissa J. Hobson","doi":"10.1088/1538-3873/ad1ba7","DOIUrl":null,"url":null,"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<sup>−1</sup>, and 75 from other instruments with a typical precision of 30–100 m s<sup>−1</sup>. 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 <monospace>REBOUND</monospace> simulations of hierarchical triples with a range of inner periods, mass ratios, eccentricities, and orientations, we show that plausible inner binaries with periods <italic toggle=\"yes\">P</italic>\n<sub>inner</sub> ≳ 1.5 days would have produced larger deviations from a Keplerian orbit than observed. Binaries with <italic toggle=\"yes\">P</italic>\n<sub>inner</sub> ≲ 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 <inline-formula>\n<tex-math>\n<?CDATA $f\\left({M}_{\\mathrm{BH}}\\right)=3.9358\\pm 0.0002\\,{M}_{\\odot }$?>\n</tex-math>\n<mml:math overflow=\"scroll\"><mml:mi>f</mml:mi><mml:mfenced close=\")\" open=\"(\"><mml:mrow><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>BH</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:mfenced><mml:mo>=</mml:mo><mml:mn>3.9358</mml:mn><mml:mo>±</mml:mo><mml:mn>0.0002</mml:mn><mml:mspace width=\"0.25em\"></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math>\n<inline-graphic xlink:href=\"paspad1ba7ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\n</inline-formula>—about 7000<italic toggle=\"yes\">σ</italic> above the ∼2.5 <italic toggle=\"yes\">M</italic>\n<sub>⊙</sub> maximum neutron star mass. Including the inclination constraint from Gaia astrometry, this implies a BH mass of <italic toggle=\"yes\">M</italic>\n<sub>BH</sub> = 9.27 ± 0.10 <italic toggle=\"yes\">M</italic>\n<sub>⊙</sub>.","PeriodicalId":20820,"journal":{"name":"Publications of the Astronomical Society of the Pacific","volume":null,"pages":null},"PeriodicalIF":3.3000,"publicationDate":"2024-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Publications of the Astronomical Society of the Pacific","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1088/1538-3873/ad1ba7","RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"ASTRONOMY & ASTROPHYSICS","Score":null,"Total":0}
引用次数: 0
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 Pinner ≳ 1.5 days would have produced larger deviations from a Keplerian orbit than observed. Binaries with Pinner ≲ 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 fMBH=3.9358±0.0002M⊙—about 7000σ above the ∼2.5 M⊙ maximum neutron star mass. Including the inclination constraint from Gaia astrometry, this implies a BH mass of MBH = 9.27 ± 0.10 M⊙.
期刊介绍:
The Publications of the Astronomical Society of the Pacific (PASP), the technical journal of the Astronomical Society of the Pacific (ASP), has been published regularly since 1889, and is an integral part of the ASP''s mission to advance the science of astronomy and disseminate astronomical information. The journal provides an outlet for astronomical results of a scientific nature and serves to keep readers in touch with current astronomical research. It contains refereed research and instrumentation articles, invited and contributed reviews, tutorials, and dissertation summaries.