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Abell 1201: detection of an ultramassive black hole in a strong gravitational lens

Nightingale, JW; Smith, Russell J; He, Qiuhan; O’Riordan, Conor M; Kegerreis, Jacob A; Amvrosiadis, Aristeidis; Edge, Alastair C; Etherington, Amy; Hayes, Richard G; Kelly, Ash; Lucey, John R; Massey, Richard J

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Dr Qiuhan He
Post Doctoral Research Associate

Conor M O’Riordan

Jacob A Kegerreis

Richard G Hayes

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Ashley Kelly
PGR Student Doctor of Philosophy


Supermassive black holes (SMBHs) are a key catalyst of galaxy formation and evolution, leading to an observed correlation between SMBH mass MBH and host galaxy velocity dispersion σe. Outside the local Universe, measurements of MBH are usually only possible for SMBHs in an active state: limiting sample size and introducing selection biases. Gravitational lensing makes it possible to measure the mass of non-active SMBHs. We present models of the z = 0.169 galaxy-scale strong lens Abell 1201. A cD galaxy in a galaxy cluster, it has sufficient ‘external shear’ that a magnified image of a z = 0.451 background galaxy is projected just ∼1 kpc from the galaxy centre. Using multiband Hubble Space Telescope imaging and the lens modelling software PYAUTOLENS, we reconstruct the distribution of mass along this line of sight. Bayesian model comparison favours a point mass with MBH = 3.27 ± 2.12 × 1010 M⊙ (3σ confidence limit); an ultramassive black hole. One model gives a comparable Bayesian evidence without an SMBH; however, we argue this model is nonphysical given its base assumptions. This model still provides an upper limit of MBH ≤ 5.3 × 1010 M⊙, because an SMBH above this mass deforms the lensed image ∼1 kpc from Abell 1201’s centre. This builds on previous work using central images to place upper limits on MBH, but is the first to also place a lower limit and without a central image being observed. The success of this method suggests that surveys during the next decade could measure thousands more SMBH masses, and any redshift evolution of the MBH−σe relation. Results are available at


Nightingale, J., Smith, R. J., He, Q., O’Riordan, C. M., Kegerreis, J. A., Amvrosiadis, A., …Massey, R. J. (2023). Abell 1201: detection of an ultramassive black hole in a strong gravitational lens. Monthly Notices of the Royal Astronomical Society, 521(3), 3298-3322.

Journal Article Type Article
Acceptance Date Jan 19, 2023
Online Publication Date Mar 29, 2023
Publication Date 2023-05
Deposit Date Mar 29, 2023
Publicly Available Date Mar 29, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 521
Issue 3
Pages 3298-3322


Published Journal Article (6.7 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023, The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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