The galaxy cluster Abell 1689 as seen by Hubble. The mass in the cluster acts as a gravitational lens, distorting the light from background galaxies into blueish arcs of light. Abell 1689 is relatively close by, but astronomers have now spotted clusters in the early universe via their lensing of even more remote, luminous galaxies, and have studied the star formation underway in their outer regions. Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI), G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA
The first stars appeared ~100 million years after the big bang, and ever since then stars and star formation processes have lit up the cosmos, producing heavy elements, planets, black holes etc. When the universe was ~3 billion years old (currently it is 13.8 billion years old), star formation activity peaked at rates about 10X above current levels. Why this happened, and whether the physical processes back then were different from those today or just more active (and why), are among the most pressing questions in astronomy, and are among the drivers of future facilities from large ground-based telescopes to NASA’s James Webb Space Telescope.
The local environment of a galaxy plays a critical role in regulating its star formation Eg in dense galaxy cluster environments (a cluster can contain as many as a thousand galaxies) the star formation is suppressed, consistent with the idea that interactions and other mechanisms are stripping away the raw material for new stars (the neutral gas) and sweeping it into the intergalactic environment. In the distant universe, however, the picture is murkier, and some studies have even found the opposite, perhaps explaining in part the higher star formation rates then.
CfA astronomers Matt Ashby, Brian Stalder, Tony Stark and their team have studied star formation in very dense galaxy clusters in the early universe from 6 billion years after the big bang, in an effort to resolve the issue of star formation in cluster environments. They started with ultraluminous galaxies from the earlier, 3 billion year-old epoch (or even younger), discovered with the South Pole Telescope. These more distant galaxies were detected in part because their light has been gravitationally lensed by closer clusters. They used infrared data from the Herschel and Planck Space Telescopes (and others) to examine the faint infrared signals from the clusters.
Their principal finding is star formation activity is enhanced, not suppressed, in these clusters, up to several thousand new stars are forming per year in these clusters over-and-above the normal levels for these sets of galaxies. They also find that star formation is active out to the edges of clusters, perhaps 15 million light-years across, and that the effect of this faint infrared emission needs to be taken into consideration in studies of origins of the cosmic background.
https://www.cfa.harvard.edu/news/su201607 http://phys.org/news/2016-02-star-formation-distant-galaxy-clusters.htmljCp
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