Abell 1689
Abell 1689 is a massive galaxy cluster whose gravity strongly lenses light from more distant galaxies, producing distorted arcs and multiple images.
Gravitational lens: A massive object that bends light from a more distant source through gravity. Abell 1689 acts as a gravitational lens, bending background-galaxy light into arcs.
Magnification bias: An observational selection effect in which gravitational magnification changes the apparent abundance of background sources. Its magnification makes some otherwise faint background galaxies observable.
Einstein cross: A configuration in which one distant source appears as four images around a foreground lens. It is a compact multiple-image pattern, unlike the cluster’s many extended arcs.
Galaxy cluster: A gravitationally bound system containing hundreds to thousands of galaxies, hot gas, and dark matter. Abell 1689 is a particularly massive example of this structure.
Strong gravitational lensing: Gravitational lensing that creates conspicuous arcs, rings, or multiple images when source, lens, and observer align. Its dense core produces numerous highly distorted images of distant galaxies.
High-redshift galaxy: A galaxy whose large cosmological redshift indicates that its light has traveled for billions of years. Lensing by the cluster helps astronomers study very distant galaxies behind it.
Abell catalog: A catalog of rich galaxy clusters compiled by George O. Abell and later collaborators. The cluster is one entry in the catalog that names it.
Intracluster medium: The hot, diffuse plasma filling the space between galaxies in a galaxy cluster. This X-ray-emitting gas is a major component of the cluster’s ordinary matter.
Einstein ring: A ring-shaped image formed when a distant source, gravitational lens, and observer are closely aligned. The cluster’s lensing geometry can produce near-ring structures from background sources.
Cosmic distance ladder: A sequence of astronomical methods used to measure distances across the universe. Lensed sources behind the cluster provide information about cosmological distance ratios.