Large quasar group

A concentration of quasars whose members cluster across an exceptionally large region of the universe. Its size challenges assumptions that matter is homogeneous on the largest cosmic scales.

Quasar: An extremely luminous active galactic nucleus powered by matter accreting onto a supermassive black hole. Quasars are the bright objects whose positions define the group.
Clowes–Campusano LQG: A large quasar group discovered in 1989 in a survey of quasars near the south Galactic pole. It was among the early named examples that established large quasar groups as a subject of study.
Cosmological principle: The assumption that the universe is statistically homogeneous and isotropic on sufficiently large scales. An exceptionally large group raises questions about how quickly this statistical description applies.
Large-scale structure of the universe: The distribution of galaxies, quasars, and dark matter across vast regions of the universe. Large quasar groups are one proposed feature of this broader distribution.
Redshift: The increase in wavelength of light caused by cosmic expansion or other relative motion. Quasar redshifts help estimate distances and locate group members in three dimensions.
Huge-LQG: A reported large quasar group at redshift about 1.27, announced in 2013 and estimated to span roughly four billion light-years. Its exceptional claimed extent made it a prominent test case for the meaning of cosmic homogeneity.
Cosmic homogeneity: The statistical uniformity of matter distribution when measured over sufficiently large cosmic volumes. The issue is whether a large quasar group is compatible with homogeneity at the scale measured.
Cosmic variance: The uncertainty that arises because observations sample only a finite region of a statistically varying universe. A limited survey volume can make unusual concentrations appear more decisive than they are.
Galaxy redshift survey: A systematic map of galaxies or other astronomical objects using measured redshifts and sky positions. Survey design and sampling determine which apparent quasar concentrations can be detected.
Roger Clowes: A British astronomer known for research on quasars and large quasar groups. His surveys and analyses helped identify and characterize large quasar groups.

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