Feedback on Galaxy Formation

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Science  06 Sep 2013:
Vol. 341, Issue 6150, pp. 1073-1075
DOI: 10.1126/science.1243114

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The rate of star formation in galaxies peaked about 10 billion years ago when the universe was just over 3 billion years old. It has been in decline ever since. Whereas spiral galaxies, like the Milky Way, slowly churn disks of cold gas clouds into young blue stars, giant elliptical galaxies today are dormant. Despite having developed atmospheres of tenuous, 10-million-degree gas waiting to cool and fuel star formation, most are “red and dead” (see the figure). Why they remain so is one of the great mysteries of galaxy formation. On page 1082 of this issue, Morganti et al. (1) reveal part of the answer.