Magnified Megacluster

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Science  07 Nov 2003:
Vol. 302, Issue 5647, pp. 951-953
DOI: 10.1126/science.302.5647.951e

A fortuitous alignment of a deep stellar cluster (redshift of 3.36) with a nearby cluster complex (redshift of 0.5) has created a gravitational lens of the farther cluster, which is called the Lynx arc. What is especially advantageous is that the arc is situated along a fold caustic in the lens and is thus magnified about 10 times. Fosbury et al. took advantage of this extreme magnification and obtained spectra and photometry of the arc using the Hubble Space Telescope, ROSAT, and the Keck 10-m telescope. The arc is an H II galaxy with a cluster of about a million extremely hot (between 80,000 and 120,000 K), highly ionized O stars (blue stars). This mega-cluster of stars is the largest, brightest, and hottest star-forming region observed so far and shows that starbursts were very active when the universe was only about 2 billion years old. In addition, the Lynx spectra suggest an overabundance of silicon in the cluster, and the excess silicon may be a nucleosynthetic marker of pair instability supernovae from a Population III (the first generation of stars) cluster. The progenitors of these supernovae are inferred to be supermassive stars (140 to 260 solar masses), indicating that the first-generation stars were heavyweights. — LR

Astrophys. J. 596, 797 (2003).

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