Gravitational Lensing
As light flies through the Universe, we might suppose that it will travel along a straight line. This turns out not to be the case: light rays can be bent by the effects of gravity in the Universe. Wherever there is a clump of matter, there is a slight gravitational distortion of space and time; the light that passes near such a clump will therefore be deflected. We call this bending of light “Gravitational Lensing”.
Gravitational lensing by a cluster of galaxies. The large arc-like objects are galaxy images which have been severely gravitationally lensed. Credit: NASA, ESA, the Hubble SM4 ERO Team, and ST-ECF
This leads to striking images of distant galaxies, where their appearance has been stretched and magnified by gravitational lensing. In the most extreme cases multiple images of a single background source are observed. These ‘strong’ gravitationally lenses are very rare, requiring alignments to within 1/3600th of a degree. ‘Weak’ lensing is common: every distant source is distorted slightly as it travels through our inhomogeneous Universe.
ICG researchers are using both strong and weak lensing to study the objects causing the gravitational lensing, the expansion of the Universe, and the behaviour of gravity itself.
The cosmic horseshoe gravitational lens, as observed by the Hubble Space Telescope. The mass of the orange galaxy distorts space-time so much that a single blue galaxy appears as the blue ring. (credit NASA/ESA)
ICG staff working in this field include:
