Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

September 8, 1998

A Cluster Too Far
Credit: E. J. Ostrander et al. (Carnegie Mellon U.), WFPC2, HST, NASA

Explanation: Why is this galaxy cluster so red? Nearby clusters have galaxies with colours that are much more yellow and blue. A leading explanation is that this cluster of galaxies lies so far across our universe (z~1) that cosmological time dilation significantly reddens the light. If true, this cluster might lie too far away to have formed in a dense universe, implying that our universe is not very dense. HST 035528+09435 is one of the reddest clusters found in the Hubble Space Telescope's Medium Deep Survey. Astronomers will now work to confirm the high distance to this cluster, and contemplate what it signifies about the nature of our universe.

Tomorrow's picture: Crater Copernicus

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
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