This article was accepted into the corpus but its outbound wikilinks were never NER-processed — typical at the deepest BFS hop or when the run's entity cap was reached. No expansion funnel to show.
| QSO 0957+561 | |
|---|---|
| Name | QSO 0957+561 |
| Other names | Double Quasar, 0957+561A/B |
| Type | Quasar (gravitational lens) |
| Ra | 09h57m |
| Dec | +56°1′ |
| Redshift | 1.41 (source); 0.36 (lens) |
| Constellation | Ursa Major |
| Discovered | 1979 |
QSO 0957+561 QSO 0957+561 is a double-image gravitationally lensed quasar notable for being the first widely accepted example of a macrolensed active galactic nucleus. The system has been central to observational programs involving Alan Sandage, Vera Rubin, Dennis Walsh, Robert Carswell, and Ray Weymann in the late 20th century, and has influenced studies at Harvard University, California Institute of Technology, Royal Greenwich Observatory, European Southern Observatory, and National Optical Astronomy Observatory. It remains a benchmark for time delay measurements used by teams at Space Telescope Science Institute, Max Planck Institute for Astrophysics, Princeton University, University of Cambridge, and Institute for Advanced Study.
The system consists of two bright optical images separated by roughly 6 arcseconds formed by lensing from a foreground galaxy and associated galaxy cluster. Early spectroscopy identified the background quasar at redshift z ≈ 1.41 and the primary lensing galaxy at z ≈ 0.36, connecting work from researchers at Kitt Peak National Observatory, Palomar Observatory, Mount Wilson Observatory, Keck Observatory, and Arecibo Observatory. QSO 0957+561 set observational precedents for monitoring campaigns using facilities such as the Hubble Space Telescope, Very Large Array, Chandra X-ray Observatory, ROSAT, and numerous optical telescopes.
The initial discovery of the double image was reported by observers affiliated with Royal Greenwich Observatory and follow-up spectroscopy involved teams at Cambridge University and University of Oxford. Imaging and spectroscopic confirmation engaged instruments at Palomar Observatory, Kitt Peak National Observatory, and the Anglo-Australian Telescope. Subsequent high-resolution imaging from Hubble Space Telescope and adaptive optics observations from Keck Observatory and Very Large Telescope helped delineate the lensed images and the lensing galaxy, with radio interferometry contributions from the Very Large Array and MERLIN array. Long-term photometric monitoring programs were coordinated by groups at Harvard College Observatory, Yale University, University of California, Berkeley, and Johns Hopkins University.
Lens modelling for the system has been developed by teams at Cambridge University, Princeton University, Max Planck Institute for Astrophysics, Institute of Astronomy, Cambridge, and California Institute of Technology. Models incorporate a singular isothermal sphere, elliptical potentials, external shear from the cluster environment, and multi-component mass distributions attributed to the central elliptical galaxy and cluster halo, drawing on methodologies advanced by Roger Blandford, Tommy Gold, Subrahmanyan Chandrasekhar, and modelling frameworks used at University of Chicago and Columbia University. Lens reconstructions have employed software from groups at European Southern Observatory and numerical techniques associated with Kavli Institute for Theoretical Physics collaborations.
Time delay measurements between the two images were pursued by monitoring teams at Harvard-Smithsonian Center for Astrophysics, University of Arizona, University of Michigan, and Stanford University, with important analyses by researchers connected to Space Telescope Science Institute and Max Planck Institute for Radio Astronomy. Early claimed delays stimulated controversy involving groups at Princeton University and University of Cambridge until refined analyses using cross-correlation, dispersion spectra, and Bayesian techniques from Columbia University and University of Oxford converged on a delay of order several hundred days. Variability studies incorporated campaigns employing Hubble Space Telescope imaging, Chandra X-ray Observatory spectroscopy, and radio monitoring at Very Large Array and European VLBI Network facilities.
High-resolution imaging resolved faint host galaxy features and nearby cluster members identified by spectroscopy from Keck Observatory, Gemini Observatory, and Subaru Telescope. The primary lens is associated with a giant elliptical galaxy embedded in a cluster studied by observers at Smithsonian Astrophysical Observatory and Max Planck Institute for Extraterrestrial Physics. Environmental mass contributions and line-of-sight structures have been quantified using redshift surveys carried out by teams at University of California, Santa Cruz, Carnegie Institution for Science, and National Radio Astronomy Observatory.
Multiwavelength data spanning radio, optical, infrared, and X-ray regimes were gathered by collaborations including Very Large Array, MERLIN, Hubble Space Telescope, Spitzer Space Telescope, Chandra X-ray Observatory, and ROSAT. Radio morphologies seen by Very Long Baseline Array and European VLBI Network elucidated jet structures, while infrared imaging from Spitzer Space Telescope and ground-based observatories informed extinction and lensing magnification. X-ray variability and absorption studies were pursued by teams at Harvard-Smithsonian Center for Astrophysics and Max Planck Institute for Extraterrestrial Physics.
QSO 0957+561 has been central to time-delay cosmography efforts by collaborations at Institute for Advanced Study, Princeton University, University of California, Berkeley, and Max Planck Institute for Astrophysics to infer the Hubble constant. Analyses combined lens modelling, stellar dynamics of the lens galaxy measured at Keck Observatory and Very Large Telescope, and environmental mass characterizations from cluster surveys at European Southern Observatory and Carnegie Institution for Science. Results influenced debates involving teams at Planck Collaboration, Supernova Cosmology Project, High-Z Supernova Search Team, Sloan Digital Sky Survey, and Dark Energy Survey, underscoring systematics related to mass-sheet degeneracy, line-of-sight structure, and microlensing by stars in the lens galaxy. Continued monitoring and modelling by groups at Space Telescope Science Institute, Kavli Institute for Cosmology, and Flatiron Institute aim to refine cosmological inferences.
Category:Gravitational lenses Category:Quasars