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An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing

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; Collaboration, OGLE; Barry, Richard K.; Bennett, David P.; Bond, Ian A.; Hirao, Yuki; Ishitani Silva, Stela; Kondo, Iona; Koshimoto, Naoki; Ranc, Clément; Rattenbury, Nicholas J.; Sumi, Takahiro; Suzuki, Daisuke; Tristram, Paul J.; Vandorou, Aikaterini; Collaboration, MOA; 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; Collaboration, PLANET; Gould, Andrew; Yee, Jennifer C.; Allen, Willia...

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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

OGLE Collaboration

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

MOA Collaboration

Jean-Philippe Beaulieu

Jean-Baptiste Marquette

Andrew Cole

Pascal Fouqué

Kym Hill

Stefan Dieters

Christian Coutures

Dijana Dominis-Prester

Clara Bennett

Etienne Bachelet

John Menzies

Michael Albrow

Karen Pollard

PLANET Collaboration

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

μFUN Collaboration

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

Jeremy Tregloan-Reed

Joachim Wambsganss

Olivier Wertz

MiNDSTEp Consortium

Yiannis Tsapras

Rachel A. Street

D.M. Bramich

Keith Horne

Iain A. Steele

RoboNet Collaboration


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, in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of six years, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry shows a parallactic signature of the effect of the 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_Sun 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, suggesting that the BH received a modest 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 ever for an isolated stellar-mass BH using any technique.


Sahu, K. C., Anderson, J., Casertano, S., Bond, H. E., Udalski, A., Dominik, M., …Collaboration, R. (2022). An Isolated Stellar-Mass Black Hole Detected Through Astrometric Microlensing. Astrophysical Journal, 933(1),

Journal Article Type Article
Acceptance Date Jan 31, 2022
Publication Date Jan 31, 2022
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 933
Issue 1
Publisher URL


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