Journal Article

Lensing by a singular isothermal sphere and a black hole

Shude Mao and Hans J. Witt

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 420, issue 1, pages 792-799
Published in print February 2012 | ISSN: 0035-8711
Published online January 2012 | e-ISSN: 1365-2966 | DOI:
Lensing by a singular isothermal sphere and a black hole

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Most galaxies host central supermassive black holes. As two galaxies merge, the black holes also merge. The final single black hole may suffer a kick due to asymmetric gravitational radiation and may not be at the centre of the galaxy; off-centre black holes may also be produced by other means such as sustained acceleration due to asymmetric jet power. We model the main galaxy as a singular isothermal sphere and the black hole as an off-centre point lens, and study the critical curves and caustics using complex notation. We identify the critical parameters that govern the transitions in the topology of critical curves, caustics and pseudo-caustics, and find that the number of images can be 2, 3, 4 and 5. We show examples of image configurations, including cases where three highly de-magnified images are found close to the centre. The perturbation on the image magnification due to the black hole scales linearly with its mass in the off-centre case, and quadratically when the black hole is at the centre. Such images are difficult to observe unless high-contrast and high-resolution imaging facilities (e.g. the Square Kilometre Array in the radio) become available.

Keywords: black hole physics; gravitational lensing: strong; galaxies: elliptical and lenticular, cD; galaxies: structure

Journal Article.  4088 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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