An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that the luminosity is not produced by stars. Such excess, non-stellar emissions have been observed in the radio, microwave, infrared, optical, ultra-violet, X-ray and gamma ray wavebands. A galaxy hosting an AGN is called an active galaxy. The non-stellar radiation from an AGN is theorized to result from the accretion of matter by a supermassive black hole at the center of its host galaxy.
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with very high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are clearly detectable.
A supermassive black hole is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (M☉). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way galaxy has a supermassive black hole at its center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei (AGNs) and quasars.
Amy J. Barger is an American astronomer and Henrietta Leavitt Professor of Astronomy at the University of Wisconsin–Madison. She is considered a pioneer in combining data from multiple telescopes to monitor multiple wavelengths and in discovering distant galaxies and supermassive black holes, which are outside of the visible spectrum. Barger is an active member of the International Astronomical Union.
APM 08279+5255 is a very distant, broad absorption line quasar located in the constellation Lynx. It is magnified and split into multiple images by the gravitational lensing effect of a foreground galaxy through which its light passes. It appears to be a giant elliptical galaxy with a supermassive black hole and associated accretion disk. It possesses large regions of hot dust and molecular gas, as well as regions with starburst activity.
Dr. Kimberly A. Weaver is an American astrophysics astronomer and professor. She has worked with NASA on several research projects. She is often seen on television programs about astronomy. She is an expert in the area of x-ray astronomy.
Hanny's Voorwerp, is a type of astronomical object called a quasar ionization echo. It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel while she was participating as a volunteer in the Galaxy Zoo project, part of the Zooniverse group of citizen science websites. Photographically, it appears as a bright blob close to spiral galaxy IC 2497 in the constellation Leo Minor.
Priyamvada (Priya) Natarajan is a professor in the departments of astronomy and physics at Yale University. She is noted for her work in mapping dark matter and dark energy, particularly with her work in gravitational lensing, and in models describing the assembly and accretion histories of supermassive black holes. She authored the book Mapping the Heavens: The Radical Scientific Ideas That Reveal the Cosmos.
Christopher David Impey is a British astronomer, educator, and author. He has been a faculty member at the University of Arizona since 1986. Impey has done research on observational cosmology, in particular low surface brightness galaxies, the intergalactic medium, and surveys of active galaxies and quasars. As an educator, he has pioneered the use of instructional technology for teaching science to undergraduate non-science majors. He has written many technical articles and a series of popular science books including The Living Cosmos, How It Began, How It Ends: From You to the Universe, Dreams of Other Worlds, and Humble Before the Void. He served as Vice-President of the American Astronomical Society, he is a Fellow of the American Association for the Advancement of Science, and a Howard Hughes Medical Institute Professor. He serves on the Advisory Council of METI.
NGC 4102 is an intermediate barred spiral galaxy located in the northern constellation of Ursa Major. It is visible in a small telescope and has an apparent visual magnitude of 11.2. The galaxy was discovered April 12, 1789 by William Herschel. J. L. E. Dreyer described it as "bright, pretty small, round, brighter middle and bright nucleus". This galaxy is located at a distance of 60 million light years and is receding with a heliocentric radial velocity of 837 km/s. It is a member of the Ursa Major group of galaxies.
Alice Eve Shapley is a professor at the University of California, Los Angeles (UCLA) in the Department of Physics and Astronomy. She was one of the discoverers of the spiral galaxy BX442. Through her time at University of California, Los Angeles (UCLA) she has taught Nature of the Universe, Black Holes and Cosmic Catastrophes, Cosmology: Our Changing Concepts of the Universe, Galaxies, Scientific Writing, AGNs, Galaxies, *and* Writing, and The Formation and Evolution of Galaxies and the IGM. Shapley has committed herself to over a two decades of research and publication in the interest of physics and astronomy.
Nadia Zakamska is a Russian-American astronomer who is a professor at Johns Hopkins University.
Gopal Krishna is an Indian radio astronomer and a senior professor at the National Centre for Radio Astrophysics. Known for his studies on Radio galaxies and quasars, Krishna is an elected fellow of all the three major Indian science academies viz. Indian Academy of Sciences, National Academy of Sciences, India and Indian National Science Academy. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, for his contributions to physical sciences in 1993.
Ajit Kembhavi is an Indian astrophysicist. He is presently a Professor Emeritus at the Inter-University Centre for Astronomy and Astrophysics, (IUCAA) at Pune, India, of which he was also a founder member. He also serves as a Vice President of the International Astronomical Union. He is the Principal Investigator of Pune Knowledge Cluster along with Professor L. S. Shashidhara.
Burçin Mutlu-Pakdil is a Turkish-American astrophysicist, and Assistant Professor at Dartmouth College. She formerly served as a National Science Foundation (NSF) and Kavli Institute for Cosmological Physics (KICP) Postdoctoral Fellow at the University of Chicago. Her research led to a discovery of an extremely rare galaxy with a unique double-ringed elliptical structure, which is now commonly referred to as Burcin's Galaxy. She was also a 2018 TED Fellow, and a 2020 TED Senior Fellow.
Sarah Connoran Gallagher is a professor of astronomy at the University of Western Ontario, where her research focuses on active galaxies, black holes and compact galaxy groups. From 2018 to 2022, she also served as Science Advisor to the Canadian Space Agency.
Alexey Vikhlinin is a Russian-American astrophysicist notable for achievements in the astrophysics of high energy phenomenon, namely galaxy cluster cosmology and the design of space-based X-ray observatories. He is currently a senior astrophysicist at the Smithsonian Astrophysical Observatory, part of the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts. He was recently the Science and Technology Definition Team (STDT) Community Co-chair for the Lynx X-ray Observatory, a NASA-funded Large Mission Concept Study under consideration by the 2020 Decadal Survey on Astronomy and Astrophysics.
Dara J. Norman is an astronomer and the deputy director of the Community Science and Data Center at the National Science Foundation's National Optical-Infrared Astronomy Research Laboratory (NOIRLab) in Tucson, Arizona. She is also the Association of Universities for Research in Astronomy Diversity Advocate at NOAO. Her research centers on the influence of Active Galactic Nuclei (AGN) on the evolution of galaxies. In 2020, she was inducted into the inaugural cohort of American Astronomical Society Fellows in recognition of her leadership and achievements.
Marc S. Seigar is an astrophysicist, academic and author. He is the Dean of the College of Natural Sciences and Mathematics, and a Professor of Physics and Astronomy at the University of Toledo.
Stefano Bianchi is an Italian astrophysicist who is currently an Associate Professor at the Mathematics and Physics Department of Università degli Studi Roma Tre in Rome, Italy. He is an INAF Associate and an IAU Member.
