Cloverleaf quasar

Molecular gas (notably CO) detected in the host galaxy associated with the quasar is the oldest molecular material known and provides evidence of large-scale star formation in the early universe.Thanks to the strong magnification provided by the foreground lens, the Cloverleaf is the brightest known source of CO emissionat high redshift^[1] and was also the first source at a redshift z = 2.56 to be detected with HCN^[2] or HCO⁺ emission.^[3] The 4 quasar images were originally discovered in 1984; in 1988, they were determined to be a single quasar split into four images, instead of 4 separate quasars. The X-rays from iron atoms were also enhanced relative to X-rays at lower energies. Since the amount of brightening due to gravitational lensing doesn't vary with the wavelength, this means that an additional object has magnified the X-rays. The increased magnification of the X-ray light can be explained by gravitational microlensing, an effect which has been used to search for compact stars and planets in our galaxy. Microlensing occurs when a star or a multiple star system passes in front of light from a background object. If a single star or a multiple star system in one of the foreground galaxies passed in front of the light path for the brightest image, then that image would be selectively magnified.^{[citation needed]}

The X-rays would be magnified much more than the visible lightif they came from a region around the central supermassive black hole of the lensing galaxy that was smaller than the origin region of the visible light. The enhancement of the X-rays from iron ions would be due to this same effect. The analysis indicates that the X-rays are coming from a very small region, about the size of the Solar System, around the central black hole. The visible light is coming from a region ten or more times larger. The angular size of these regions at a distance of 11 billion light years is tens of thousands times smaller than the smallest region that can be resolved by the Hubble Space Telescope. This provides a way to test models for the flow of gas around a supermassive black hole.^{[citation needed]}

Data from NICMOS and a special algorithm resolved the lensing galaxy and a partial Einstein ring. The Einstein ring represents the host galaxy of the lensed quasar.^[4]

The Cloverleaf quasar was discovered in 1988. Data on the Cloverleaf collected by the Chandra X-ray Observatory in 2004 were compared with that gathered by optical telescopes. One of the X-ray components (A) in the Cloverleaf is brighter than the others in both optical and X-ray light but was found to be relatively brighter in X-ray than in optical light. The X-rays from iron atoms were also enhanced relative to X-rays at lower energies.^{[citation needed]}

• List of quasars

• R. Barvainis; L. Tacconi; R. Antonucci; D. Alloin; P. Coleman (2002). "Extremely strong carbon monoxide emission from the Cloverleaf quasar at a redshift of 2.5". Nature. 371 (6498): 586–588. Bibcode:1994Natur.371..586B. doi:10.1038/371586a0. S2CID 4246365.
• C. M. Bradford; et al. (2009). "The Warm Molecular Gas Around the Cloverleaf Quasar". Astrophysical Journal. 705 (1): 112. arXiv:0908.1818. Bibcode:2009ApJ...705..112B. doi:10.1088/0004-637X/705/1/112. S2CID 13889803.

• Chandra at Havard CfA, "Cloverleaf Quasar: Chandra Looks Over a Cosmic Four-Leaf Clover", 20 February 2009