An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing

Creators: Sahu, Kailash C.; Anderson, Jay; Casertano, Stefano; Bond, Howard E.; Udalski, Andrzej; Dominik, Martin; Calamida, Annalisa; Bellini, Andrea; Brown, Thomas M.; Rejkuba, Marina; Bajaj, Varun; Kains, Noé; Ferguson, Henry C.; Fryer, Chris L.; Yock, Philip; Mróz, Przemek; Kozłowski, Szymon; Pietrukowicz, Paweł; Poleski, Radek; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Ulaczyk, Krzysztof; Wyrzykowski, Łukasz; Barry, Richard K.; Bennett, David P.; Bond, Ian A.; Hirao, Yuki; Silva, Stela Ishitani; Kondo, Iona; Koshimoto, Naoki; Ranc, Clément; Rattenbury, Nicholas J.; Sumi, Takahiro; Suzuki, Daisuke; Tristram, Paul J.; Vandorou, Aikaterini; Beaulieu, Jean-Philippe; Marquette, Jean-Baptiste; Cole, Andrew; Fouqué, Pascal; Hill, Kym; Dieters, Stefan; Coutures, Christian; Dominis-Prester, Dijana; Bennett, Clara; Bachelet, Etienne; Menzies, John; Albrow, Michael; Pollard, Karen; Gould, Andrew; Yee, Jennifer C.; Allen, William; Almeida, Leonardo A.; Christie, Grant; Drummond, John; Gal-Yam, Avishay; Gorbikov, Evgeny; Jablonski, Francisco; Lee, Chung-Uk; Maoz, Dan; Manulis, Ilan; McCormick, Jennie; Natusch, Tim; Pogge, Richard W.; Shvartzvald, Yossi; Jørgensen, Uffe G.; Alsubai, Khalid A.; Andersen, Michael I.; Bozza, Valerio; Calchi Novati, Sebastiano; Burgdorf, Martin; Hinse, Tobias C.; Hundertmark, Markus; Husser, Tim-Oliver; Kerins, Eamonn; Longa-Peña, Penelope; Mancini, Luigi; Penny, Matthew; Rahvar, Sohrab; Ricci, Davide; Sajadian, Sedighe; Skottfelt, Jesper; Snodgrass, Colin; Southworth, John; Tregloan-Reed, Jeremy; Wambsganss, Joachim; Wertz, Olivier; Tsapras, Yiannis; Street, Rachel A.; Bramich, D. M.; Horne, Keith; Steele, Iain A.; OGLE Collaboration; MOA Collaboration; PLANET Collaboration; µFUN Collaboration; MINDSTEP Consortium; ROBONET Collaboration

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Abstract

We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t_E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M_⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of ∼45 km s⁻¹, suggesting that the BH received a "natal kick" from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 January 28; revised 2022 May 19; accepted 2022 May 24; published 2022 July 6. Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Support for this research was provided by NASA through grants from STScI. HST data used in this paper are available from the Mikulski Archive for Space Telescopes at STScI, 82 under proposal IDs 12322, 12670, 12986, 13458, and 14783. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The MOA project is supported by JSPS KAK-ENHI grant Nos. JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, JP16H06287, 17H02871, and 19KK0082. We acknowledge the help and dedication of the late Dr. John Greenhill, who, as part of the PLANET collaboration, played a key role in the efforts of collaboration in general, and in particular running the Tasmania observatory operations. K.C.S. spent some time at the European Southern Observatory, Institute for Advanced Study, and Harvard-Smithsonian Center for Astrophysics, where some of this work was done, and thanks them for their hospitality. Ł.W. acknowledges support from the Polish NCN grant Daina No. 2017/27/L/ST9/03221. J.-P.B. acknowledges support by the University of Tasmania through the UTAS Foundation and the endowed Warren Chair in Astronomy, and support by ANR COLD-WORLDS (ANR-18-CE31-0002) at Le Centre National de la Recherche Scientifique (CNRS) in Paris and the Laboratoire d'astrophysique de Bordeaux. U.G.J. acknowledges funding from the European Union H2020-MSCA-ITN-2019 under grant No. 860470 (CHAMELEON) and from the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant no. NNF19OC0057374. L.M. acknowledges support from the "Fondi di Ricerca Scientificad'Ateneo 2021" of the University of Rome "Tor Vergata." D.D.P. acknowledges support by the University of Rijeka through the grant uniri-prirod-18-48. T.C.H. acknowledges financial support from the National Research Foundation (NRF; No. 2019R1I1A1A 01059609). Y.T. acknowledges the support of DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (TS 356/3-1). Note added: After our paper was submitted, a study by Lam et al. (2022) that includes an independent investigation of MOA-11-191/OGLE-11-462 was posted on arXiv. We have not used any of the measurements or results from that paper in our analysis. Facilities: HST (WFC3). This research is based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

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