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.

2001 February 22
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3C294: Distant X-Ray Galaxy Cluster
Credit: A. Fabian (IoA Cambridge) et al., NASA

Explanation: Large clusters of galaxies are the most massive objects in the universe. Astronomers now realize that a hallmark of these cosmic behemoths are gas clouds with temperatures of tens of millions of degrees that pervade the clusters and radiate strongly in x-rays. This Chandra Observatory image centred on a radio galaxy catalogued as 3C294 indeed reveals the telltale hot x-ray gas in an hourglass shaped region surrounding the dominant galaxy and shows the presence of a massive galaxy cluster in the distant universe. Here the picture is colour-coded by x-ray energy, red for low, green for medium, and blue for high energy x-rays. The cluster associated with 3C294 is 10 billion light-years away making it the most distant x-ray galaxy cluster ever detected. Objects at that extreme distance existed when the universe was young, a mere 20 percent of its present age. Impressively, this observation demonstrates that even at those early times massive clusters of galaxies were already present.

Tomorrow's picture: M55 in colour

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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& Michigan Tech. U.