12 February 2004
Galaxies behaving oddly
The gravity of a galaxy can act like a distorting lens, producing optical illusions such as multiple images of background objects. Since the first example of this gravitational lensing effect was observed in 1979 there has been a persistent paradox. Theorists expect there to be an odd number of images, including a fairly faint central image appearing near the middle of the lens. For many years there was no sign of the 'missing' central images. A number of candidates have recently been found but a confirmed sighting remains elusive. Winn et al. now present the most secure identification yet of a central image, based on radio observations of one of those candidates. It is faint, as expected, and its existence allows a number of interesting conclusions to be drawn about the nucleus of the lensing galaxy, including a maximum possible mass for its central black hole.
The central image of a gravitationally lensed
quasar
JOSHUA N. WINN, DAVID RUSIN & CHRISTOPHER S. KOCHANEK
Nature 427, 613–615 (2004); doi:10.1038/nature02279
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