Searching for Dark Matter in a Galaxy Cluster

This rich galaxy cluster, catalogued as Cl 0024+17, is allowing astronomers to probe the distribution of dark matter in space. The blue streaks near the center of the image are the smeared images of very distant galaxies that are not part of the cluster. The distant galaxies appear distorted because their light is being bent and magnified by the powerful gravity of Cl 0024+17, an effect called gravitational lensing.

Dark matter cannot be seen because it does not shine or reflect light. Astronomers can only detect its influence by how its gravity affects light. By mapping the distorted light created by gravitational lensing, astronomers can trace how dark matter is distributed in the cluster. While mapping the dark matter, astronomers found a dark-matter ring near the cluster's center. The ring's discovery is among the strongest evidence that dark matter exists.

The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys.

About the colours

This image is a composite of many separate exposures made by the ACS instrument on the Hubble Space Telescope. In total, six filters were used to sample light from broad and narrow wavelengths. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are: Blue: F435W (B) + F475W (g) Green: F555W (V) + F625W (r) Red: F775W (i) + F850LP (z)

About the data

The ACS data was from the HST proposal 10325 : H. Ford (Johns Hopkins University), N. Benitez (Johns Hopkins University/Instituto de Astrofisica de Andalucia), T. Broadhurst (Tel Aviv University - Wise Observatory), R. White (STScI), K. Zekser (Johns Hopkins University), and D. Coe (Johns Hopkins University/Instituto de Astrofisica de Andalucia).

The science team includes: M.J. Jee and H. Ford (Johns Hopkins University), G. Illingworth (UCO/Lick Observatory, University of California, Santa Cruz), R. White (STScI), T. Broadhurst (Tel Aviv University - Wise Observatory), D. Coe (Johns Hopkins University/Instituto de Astrofisica de Andalucia), G. Meurer and A. van der Wel (Johns Hopkins University), N. Benitez (Johns Hopkins University/Instituto de Astrofisica de Andalucia), J. Blakeslee (Washington State University), R. Bouwens (UCO/Lick Observatory, University of California, Santa Cruz), L. Bradley , R. Demarco, N. Homeier, A. Martel, and S. Mei (Johns Hopkins University).