An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing

Kailash C. Sahu , Jay Anderson , Stefano Casertano , Howard E. Bond , Andrzej Udalski , Martin Dominik , Annalisa Calamida , Andrea Bellini , Thomas M. Brown , Marina Rejkuba , Varun Bajaj , Noé Kains , Henry C. Ferguson , Chris L. Fryer , Philip Yock , Przemek Mróz , Szymon Kozłowski , Paweł Pietrukowicz , Radek Poleski , Jan Skowron , Igor Soszyński , Michał K. Szymański , Krzysztof Ulaczyk , Łukasz Wyrzykowski , Richard K. Barry , David P. Bennett , Ian A. Bond , Yuki Hirao , Stela Ishitani Silva , Iona Kondo , Naoki Koshimoto , Clément Ranc , Nicholas J. Rattenbury , Takahiro Sumi , Daisuke Suzuki , Paul J. Tristram , Aikaterini Vandorou , Jean-Philippe Beaulieu , Jean-Baptiste Marquette (1) , Andrew Cole , Pascal Fouqué (2) , Kym Hill , Stefan Dieters , Christian Coutures (3) , Dijana Dominis-Prester , Clara Bennett , Etienne Bachelet , John Menzies , Michael Albrow , Karen Pollard , Andrew Gould , Jennifer C. Yee , William Allen , Leonardo A. Almeida , Grant Christie , John Drummond , Avishay Gal-Yam , Evgeny Gorbikov , Francisco Jablonski , Chung-Uk Lee , Dan Maoz , Ilan Manulis , Jennie Mccormick , Tim Natusch , Richard W. Pogge , Yossi Shvartzvald , Uffe G. Jørgensen , Khalid A. Alsubai , Michael I. Andersen , Valerio Bozza , Sebastiano Calchi Novati , Martin Burgdorf , Tobias C. Hinse , Markus Hundertmark , Tim-Oliver Husser , Eamonn Kerins , Penelope Longa-Peña , Luigi Mancini , Matthew Penny , Sohrab Rahvar , Davide Ricci , Sedighe Sajadian , Jesper Skottfelt , Colin Snodgrass , John Southworth , Jeremy Tregloan-Reed , Joachim Wambsganss , Olivier Wertz , Yiannis Tsapras , Rachel A. Street , D. M. Bramich , Keith Horne , Iain A. Steele

1 LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]
2 IRAP - Institut de recherche en astrophysique et planétologie
3 IAP - Institut d'Astrophysique de Paris

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. *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.

Keywords: Black holes; Gravitational microlensing; Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies; Astrophysics - High Energy Astrophysical Phenomena

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

Kailash C. Sahu, Jay Anderson, Stefano Casertano, Howard E. Bond, Andrzej Udalski, et al.. An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing. The Astrophysical Journal, 2022, 933, ⟨10.3847/1538-4357/ac739e⟩. ⟨insu-03748250⟩