This image shows a distant object which is gravitationally lensed by the cluster of galaxies AC114. It was the result of a six-hour time exposure with the HST. The inset at the upper right shows a ground based photograph of AC 114. The rectangle marks the field of view in the HST image.
The lensed object appears to be a bright galaxy located far beyond AC114. The lensing action distorts and splits the light of the distant galaxy so that it appears as the two bright elongated images at upper left and lower right in the HST picture. The two lensed images show a distinct mirror-symmetry and have identical color. The two smaller objects at the center of the HST view are thought to be galaxies in AC114, much closer than the lensed galaxy, and unrelated to it.
In this case, the action of a gravitational lens has magnified the distant galaxy so that it appears larger than it would if it were not gravitationally lensed.
Careful analysis of the HST images such as this can give the distribution of mass necessary to produce the observed gravitationally lensed images. Comparison of that calculated mass distribution with the observed distribution of luminous galaxies reveals how much 'dark matter' must be present in the cluster.
Camara: WF/PC-1
Credit: R. Ellis (University of Cambridge),
and NASA
