Distant Glowing Objects: Quest for Quasars

Dear Colleagues,

Quasars are a major class of active galactic nuclei (AGN). They are extremely small, bright and distant, and they often display relativistic jets that maintain their coherence and integrity from the very core of the AGN where they are produced, out to kiloparsecs at the distal end. They may also be highly variable. Much of the optical radiation is found in emission lines. Quasars, typically point-like, have been observed to radiate at all frequencies, from radio to extremely high-energy gamma ray (TeV) energies.

The standard interpretation of AGN is of a supermassive black hole (from millions to billions of solar masses) surrounded by an accretion disk with the swirling material falling into the black hole. This is a description of the conversion of gravitational potential energy to radiant energy.  By studying these objects, we learn about the early Universe (because they are so distant at high redshift), galactic evolution, the radiation mechanisms involved (e.g., synchrotron, inverse Compton), the production of jets and beams, and even as a probe of the intergalactic medium (IGM) obtained from observations of the interaction of the jets with the IGM.

In recent times, we have developed technologies, typically in high-energy astrophysics, which often involve international collaborations, that are opening up entire new areas of astrophysics.  One is the new field of gravitational radiation, which has had many successes over the past five years; another is neutrino telescopes; and another is Cherenkov telescopes, which are able to observe astrophysical electromagnetic radiation at TeV energies. The quest to understand quasars is a very big part of all of this research activity.

Thus, gravitational radiation and binary supermassive black holes, jets, TeV energies, emission line radiation, and neutrinos and other particles are all astrophysical phenomena that can now be explored by emerging technologies.  Frontier quasar research is welcomed, and therefore the scope and purpose of this Special Issue is to combine these technologies with the science of supermassive black holes, as best exemplified by quasars.

Prof. Dr. Alberto C. Sadun
Dr. Atreya Acharyya
Guest Editors

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