Quasars

Quasars
ESO/M. Kornmesser · CC BY 4.0 · source
Name	Quasars
Type	Active galactic nucleus

Quasars Quasars are extremely luminous active galactic nuclei observed at high redshift, powered by accretion onto supermassive black holes. They were identified through radio and optical surveys and have played central roles in studies by institutions and observatories worldwide. Historically linked to discoveries at observatories and major surveys, quasars connect to many topics in modern astrophysics and cosmology.

Overview and Discovery

The first recognized objects later classified among the brightest active galactic nuclei were found in early radio surveys such as those by Harvard College Observatory, Cavendish Laboratory, Jodrell Bank Observatory, and Arecibo Observatory and were given catalog identifiers from projects like the Third Cambridge Catalogue and the Palomar Observatory Sky Survey; follow-up optical spectroscopy at facilities including Mount Wilson Observatory, Palomar Observatory, Kitt Peak National Observatory, and Lick Observatory revealed emission lines with large redshifts, prompting theoretical work at institutions such as California Institute of Technology, Institute for Advanced Study, University of Cambridge, and Princeton University. Early interpreters included researchers associated with Royal Greenwich Observatory, Yerkes Observatory, University of Chicago, and the Max Planck Institute for Astronomy, while contemporaneous developments in radio astronomy by teams at Bell Labs, Jet Propulsion Laboratory, and CERN informed classification schemes. The discovery epoch intersects histories of projects like the Sloan Digital Sky Survey, the Two Micron All Sky Survey, and the Large Bright Quasar Survey and motivated instrumentation advances at facilities including Very Large Array, Very Long Baseline Array, Atacama Large Millimeter Array, and Hubble Space Telescope.

Physical Characteristics

Quasars exhibit extreme bolometric luminosities measured by instruments aboard missions such as Chandra X-ray Observatory, XMM-Newton, Spitzer Space Telescope, Fermi Gamma-ray Space Telescope, and Swift Observatory and are hosted by galaxies studied at observatories like Keck Observatory, Gemini Observatory, Subaru Telescope, and European Southern Observatory. Their central engines are supermassive black holes with masses inferred using techniques developed at Harvard–Smithsonian Center for Astrophysics, Max Planck Institute for Astrophysics, and Space Telescope Science Institute; mass estimates use relationships calibrated by work from groups at University of California, Berkeley, Ohio State University, and Columbia University. Surrounding structures include accretion disks modeled in frameworks originating at Princeton University, coronal regions probed via campaigns coordinated by National Radio Astronomy Observatory and Institute of Radio Astronomy of Bologna, and relativistic jets observed by collaborations such as MOJAVE and facilities like European VLBI Network, with host galaxy interactions studied by teams at Johns Hopkins University and Carnegie Institution for Science.

Emission Mechanisms and Spectra

Quasar spectra show broad and narrow emission lines first analyzed by spectroscopists at Royal Society, Royal Astronomical Society, and laboratories linked to University of Oxford and Cambridge University Press-era groups; line diagnostics reference transitions catalogued in atlases used by National Optical Astronomy Observatory and informed by atomic physics from CERN and Lawrence Berkeley National Laboratory. Continuum emission arises from processes modeled in papers authored at Massachusetts Institute of Technology, Cornell University, University of California, Santa Cruz, and University of Arizona; thermal emission from accretion disks, non-thermal synchrotron radiation from jets, and inverse Compton scattering have been invoked by theorists associated with Stanford University, Yale University, Rutgers University, and University of Michigan. Spectroscopic surveys by Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey, and DEEP2 Redshift Survey have mapped emission-line properties and enabled reverberation mapping programs coordinated by groups at Ohio State University, University of Maryland, and University of Edinburgh.

Classification and Types

Quasar classifications (including radio-loud and radio-quiet designations) were refined through work at National Radio Astronomy Observatory, Cavendish Laboratory, and Harvard–Smithsonian Center for Astrophysics and through optical taxonomy promoted by collaborations between European Southern Observatory and Instituto de Astrofísica de Canarias. Subclasses such as broad absorption line objects were characterized in studies from Max Planck Institute for Extraterrestrial Physics, narrow-line Seyfert 1 analogs were examined by researchers at Osservatorio Astronomico di Brera and University of Tokyo, and blazar-like quasars were linked to monitoring campaigns by Fermi Gamma-ray Space Telescope teams and the Whole Earth Blazar Telescope consortium. Luminosity functions and evolutionary tracks were quantified by groups at Space Telescope Science Institute, Kavli Institute for Cosmology, and Institute for Theory and Computation.

Role in Galaxy Evolution and Cosmology

Quasars have been used as probes of the intergalactic medium in programs led by European Southern Observatory, Sloan Digital Sky Survey, and Keck Observatory and inform models developed at Princeton University, Max Planck Institute for Astrophysics, and Lawrence Livermore National Laboratory for feedback processes linking active nuclei to host galaxy star formation seen in surveys by Hubble Space Telescope, Spitzer Space Telescope, and James Webb Space Telescope teams. Their luminosity and redshift distribution constrained cosmological parameters in analyses by collaborations involving Planck (spacecraft), Wilkinson Microwave Anisotropy Probe, and Dark Energy Survey, while absorption-line studies toward high-redshift quasars have been pivotal in measurements carried out by European Southern Observatory and Keck Observatory groups of reionization epochs and chemical enrichment addressed by researchers at Institute of Astronomy, Cambridge and California Institute of Technology.

Observation Techniques and Surveys

Detection and characterization rely on multiwavelength campaigns executed by consortia such as Sloan Digital Sky Survey, Fermi Gamma-ray Space Telescope teams, Chandra X-ray Observatory groups, Atacama Large Millimeter Array collaborations, and facilities including Very Large Array, Very Long Baseline Array, Green Bank Observatory, and Parkes Observatory. Time-domain programs such as those coordinated by Zwicky Transient Facility, Pan-STARRS, Large Synoptic Survey Telescope, and All-Sky Automated Survey for SuperNovae monitor variability, while high-resolution spectroscopy from Keck Observatory, Subaru Telescope, and European Southern Observatory enables black hole mass estimates and host-galaxy decomposition pursued by researchers at Johns Hopkins University, University of California, Santa Cruz, and Imperial College London.

Open Questions and Theoretical Challenges

Outstanding problems include details of angular momentum transport in accretion disks formulated in studies at Princeton Plasma Physics Laboratory and Max Planck Institute for Astrophysics, the triggering of quasar activity in merger simulations by teams at University of Arizona and University of Massachusetts Amherst, the physics of relativistic jet launching investigated at Stanford University, Massachusetts Institute of Technology, and University of Cambridge, and the role of quasar feedback in galaxy quenching modeled by groups at Harvard University, University of California, Berkeley, and Columbia University. Future progress depends on instrumentation and missions developed by European Space Agency, National Aeronautics and Space Administration, SpaceX, and collaborative surveys organized by Sloan Digital Sky Survey and Large Synoptic Survey Telescope-era teams.

Category:Active galactic nuclei