Galactic Blowup

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Science  09 Oct 2009:
Vol. 326, Issue 5950, pp. 206
DOI: 10.1126/science.326_206b

The deflection of light in the gravitational field of massive objects causes clusters of galaxies to act as cosmic lenses, magnifying and distorting the light of the galaxies that lie behind them. By analyzing Hubble Space Telescope archival images of the cluster MACS J1149.5+2223, Zitrin and Broadhurst have identified the most powerful gravitational lens yet: It magnifies a background spiral galaxy 200 times (summed over five multiple images). Distant galaxies normally appear as thin distorted arcs around the centers of clusters. In the case of this cluster, however, the lensed images of a background spiral galaxy are large and appear relatively undistorted, implying a nearly uniform mass distribution in the center of the cluster. The authors constructed a model of the mass distribution of the cluster to reproduce the lensed images they could readily identify, and they were then able to use it to predict the location of other images, ultimately identifying a total of 10 sets of multiple images of background galaxies. The refined model that reproduces all of these images is at odds with predictions made by simulations of the evolution of galaxies and associated large-scale distribution, thereby challenging our current theoretical models for the formation of structure in the universe.

Astrophys. J. 703, L132 (2009).

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