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An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing


Sahu, KC and Anderson, J and Casertano, S and Bond, HE and Udalski, A and Dominik, M and Calamida, A and Bellini, A and Brown, TM and Rejkuba, M and Bajaj, V and Kains, N and Ferguson, HC and Fryer, CL and Yock, P and Mroz, P and Kozlowski, S and Pietrukowicz, P and Poleski, R and Skowron, J and Soszynski, I and Szymanski, MK and Ulaczyk, K and Wyrzykowski, A and Barry, RK and Bennett, DP and Bond, IA and Hirao, Y and Silva, SI and Kondo, I and Koshimoto, N and Ranc, C and Rattenbury, NJ and Sumi, T and Suzuki, D and Tristram, PJ and Vandorou, A and Beaulieu, JP and Marquette, JB and Cole, A and Fouque, P and Hill, K and Dieters, S and Coutures, C and Dominis-Prester, D and Bennett, C and Bachelet, E and Menzies, J and Albrow, M and Pollard, K and Gould, A and Yee, JC and Allen, W and Allen, LA and Christie, G and Drummond, J and Gal-Yam, A and Gorbikov, E and Jablonski, F and Lee, CU and Maoz, D and Manulis, I and McCormick, J and Natusch, T and Pogge, RW and Shvartzvald, Y and Jorgensen, UG and Alsubai, KA and Andersen, MI and Bozza, V and Novati, SC and Burgdorf, M and Hinse, TC and Hundertmark, M and Husser, TO and Kerins, E and Longa-Pena, P and Mancini, L and Penny, M and Rahvar, S and Ricci, D and Sajadian, S and Skottfelt, J and Snodgrass, C and Southworth, J and Tregloan-Reed, J and Wambsganss, J and Wertz, O and Tsapras, Y and Street, RA and Bramich, DM and Horne, K and Steele, IA and Sahu, KC, OGLE Collaboration, MOA Collaboration, PLANET Collaboration, μFUN Collaboration, MiNDSTEp Consortium and RoboNet Collaboration, An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing, Astrophysical Journal, 933, (1) Article 83. ISSN 0004-637X (2022) [Refereed Article]

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DOI: doi:10.3847/1538-4357/ac739e


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 (tE ≃ 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.

Item Details

Item Type:Refereed Article
Keywords:gravitational microlensing, black holes
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Beaulieu, JP (Dr Jean-Philippe Beaulieu)
UTAS Author:Cole, A (Professor Andrew Cole)
UTAS Author:Hill, K (Dr Kym Hill)
UTAS Author:Dieters, S (Dr Stefan Dieters)
UTAS Author:Coutures, C (Dr Christian Coutures)
ID Code:154895
Year Published:2022
Funding Support:Australian Research Council (DP200101909)
Web of Science® Times Cited:2
Deposited By:Physics
Deposited On:2023-01-18
Last Modified:2023-01-18

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