Quasar quartet embedded in giant nebula reveals rare massive structure in distant universe

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Science  15 May 2015:
Vol. 348, Issue 6236, pp. 779-783
DOI: 10.1126/science.aaa5397

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In a cluster of protogalaxies far, far away

Astronomers constantly scour the sky for astronomical objects that can provide insight and constrain their models and simulations of galaxy evolution. Hennawi et al. surveyed the ancient sky at an epoch when the universe was half its age for nebulae: large clouds of ionized hydrogen. They stumbled across a system containing four active galactic nuclei, or quasars; objects that are thought to be the progenitors of galaxies. Finding a nebula with a rare quadruple quasar system embedded within it allows detailed spectroscopic and motional studies that may help to refine current models of galaxy and galaxy cluster formation.

Science, this issue p. 779


All galaxies once passed through a hyperluminous quasar phase powered by accretion onto a supermassive black hole. But because these episodes are brief, quasars are rare objects typically separated by cosmological distances. In a survey for Lyman-α emission at redshift z ≈ 2, we discovered a physical association of four quasars embedded in a giant nebula. Located within a substantial overdensity of galaxies, this system is probably the progenitor of a massive galaxy cluster. The chance probability of finding a quadruple quasar is estimated to be ∼10−7, implying a physical connection between Lyman-α nebulae and the locations of rare protoclusters. Our findings imply that the most massive structures in the distant universe have a tremendous supply (≃1011 solar masses) of cool dense (volume density ≃ 1 cm−3) gas, which is in conflict with current cosmological simulations.

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