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	Active galactic nucleus - Wikipedia, the free encyclopedia
		An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas.
		This model also explains the different types of active galactic nuclei, which are believed to all be due to the same type of source, but can appear quite different depending on the angle the source makes to the earth, and the amount of gas and dust available to be fed into the fl hole.
		AGN with jets have an additional component of nuclear X-ray emission originating in the jet: this may dominate in blazars and core-dominated quasars.
	en.wikipedia.org /wiki/Active_galactic_nuclei (731 words)

	Active Galaxies and Quasars - Introduction and Glossary
		The recognition of active galactic nuclei may be conveniently traced to three discoveries, which taught us distinct aspects of the phenomenon as well as how they might be linked.
		Seyfert nuclei were divided into two classes (1 and 2, with the panache for which astronomers are so famous) by Ed Khachikian and Daniel Weedman, based on whether all their emission lines had similar amounts of broadening.
		Some of these have been shown to be low-luminosity active galactic nuclei, perhaps an extension of Seyfert activity to the lowest levels and implying that the whole phenomenon of nuclear activity occurs in a significant fraction of bright galaxies.
	www.astr.ua.edu /keel/agn/text.html (3696 words)

	Active Galaxies and Quasars - Introduction
		Active galaxies are galaxies which have a small core of emission embedded in an otherwise typical galaxy.
		Active galaxies are intensely studied at all wavelengths.
		The AGN's observed at higher energies form a subclass of AGNs known as blazars; a blazar is believed to be an AGN which has one of its relativistic jets pointed toward the Earth so that what we observe is primarily emission from the jet region.
	imagine.gsfc.nasa.gov /docs/science/know_l1/active_galaxies.html (1211 words)

	Active Galactic Nuclei (Site not responding. Last check: 2007-11-01)
		AGN which have about the same luminosity than the host galaxy are called Seyfert galaxies.
		AGN have the peculiarity to emit electro-magnetic radiation over a very broad spectral domain from the infrared to the X-rays.
		To explain the different spectral components of an AGN, it is necessary to refer to many different physical emission processes (synchrotron emission in the radio, inverse comptonization in the X-rays, thermal dust emission in the infrared).
	obswww.unige.ch /~turler/hea/agn.html (511 words)

	AGN & the Amateur
		The observation and study of Active Galactic Nuclei (AGN) is a fairly recent branch of astronomy.
		While AGN remain exotic objects and the majority are only detectable with the largest telescopes and most sophisticated equipment, a few of the brighter ones are accessible to the amateur observer, and the contribution of the dedicated amateur can be of a significant benefit to the professional astronomer.
		Active galactic nuclei offer a wonderful challenge to the serious amateur observer who wishes to contribute in his or her small way to an area of science in which the professionals welcome help, if carefully provided.
	www.garypoyner.pwp.blueyonder.co.uk /agn.html (3902 words)

	Active Galactic Nuclei
		Active galaxy nuclei (AGNs) are those galaxies whose radiation are mainly produced in their nuclei.
		Starting with this model, is possible to understand most of the different AGN types as consequences of different viewing angles with respect to the rotation axis and of the presence or absence of jets.
		In radio-loud AGN viewed at large angle, the torus obscures the clouds that are close to the fl hole.
	www.gae.ucm.es /~marcos/tesina/html/node13.html (1002 words)

	AGN - Wikipedia, the free encyclopedia
		AGN is also a call sign for All Games Radio
		AGN is the acronym for Aerojet General Nucleonics (San Ramon, California), who produced the AGN-201 Research Nuclear Reactor
		This page disambiguates a three-character combination which might be any or all of an abbreviation, an acronym, an initialism, a word in English, or a word in another language.
	en.wikipedia.org /wiki/AGN (123 words)

	Galaxy Collisions: 8. Active Galactic Nuclei in Collisional Galaxies.
		The primary difficulty with approaching the problem from this direction is that (luminous) AGN are not as common as they used to be when the universe was younger.
		A variation of this model, in which a supermassive fl hole at the heart of the AGN is fueled by the "super" mass loss resulting from the super-starburst, was studied by Norman and Scoville (1988).
		AGN variability is accounted for by frequent supernova explosions and interactions of supernova remnants with the dense, turbulent environment.
	www.public.iastate.edu /~curt/cg/section8.html (3099 words)

	Amazon.de: Active Galactic Nuclei: From the Central Black Hole to the Galactic Environment (Princeton Series in ... (Site not responding. Last check: 2007-11-01)
		This is the first comprehensive treatment of active galactic nuclei - the cosmic powerhouses at the core of many distant galaxies.
		The term active galactic nuclei refers to quasars, radio galaxies, Seyfert galaxies, blazars, and related objects, all of which are believed to share a similar central engine - a supermassive fl hole many times the mass of the Sun.
		His new book "Active Galactic Nuclei: From the Central Black Hole to the Glactic Environment" is a great reference source for astrophyisics, especially in Active Galactic Nuclei.
	www.amazon.de /Active-Galactic-Nuclei-Environment-Astrophysics/dp/0691011516 (650 words)

	Active Galactic Nuclei
		AGN Magnetic Energy is important in Structure Formation.
		The two largest subclasses of AGNs are Seyfert galaxies and quasars, and the distinction between them is to some degree a matter of semantics.
		The scale of the Galactic wind here 1.5 Mpc, is not a critical parameter, since the calculations show that most of the bending happens within the first few 100 kpc.
	www.valdostamuseum.org /hamsmith/AGN.html (2275 words)

	Activity in Galactic Nuclei
		In radio-loud nuclei, relativistic jets of material are ejected along the polar axis of the fl hole and in some cases have sufficient energy to escape into intergalactic space as classical double-lobed sources.
		The phenomenology of nuclei is very varied, and their nuclear properties are distributed over many orders of magnitude.
		The radio signature of a fl hole in a galactic nucleus is generally taken as the presence of an unresolved core component with a flat radio spectrum and variable flux density, and a jet, or jets, emanating from the central core.
	www.skatelescope.org /science/node7.html (2084 words)

	Active Galaxies
		In ~10% of the AGN, the MBH + accretion disk somehow produce narrow beams of energetic particles and magnetic fields, and eject them outward in opposite directions away from the disk.
		Radio galaxies, quasars, and blazars are AGN with strong jets, which can travel outward into large regions of intergalactic space.
		Active Galactic Nuclei observed at high (>100 MeV) energies form a subclass known as blazars; a blazar is believed to be an AGN which has one of its relativistic jets pointed toward the Earth so that the emission we observe is dominated by phenomena occurring in the jet region.
	imagine.gsfc.nasa.gov /docs/science/know_l2/active_galaxies.html (1043 words)

	Bill Keel's Publication List
		The Active Nucleus of M81 and its History, Astron.J. High-Resolution Observations of the Multicomponent Nucleus of NGC 5929, Andrew S. Wilson and William C. Keel, Astron.J. A Spiral Galaxy at z=0.366 Which Overlaps the Image of the Quasar 4C 39.47, Paul Hintzen, W. Romanishin, Craig Foltz, and William Keel, Astrophys.
		The Stellar Population in the Wolf-Rayet Knot in NGC 5430, Astron.
		AGN in Lyman alpha Blobs: Ubiquitous and Irrelevant, R.E. White III,.
	www.astr.ua.edu /keel/publist.html (5555 words)

	MSSL Extragalactic Group - AGN Beginners Guide (Site not responding. Last check: 2007-11-01)
		The nucleus of a galaxy is said to be `active' if it appears that the light which we measure is greater than that which can be emitted by stars alone.
		The rate at which the light from an AGN can change indicates that this enormous mass is contained within a region less than one light-day across.
		Weak, or low-luminosity, AGN are sometimes powered by regions which are dominated by intensive bursts of star formation - these are known as `Starburst Galaxies' - see the section on Narrow Emission Line Galaxies
	www.mssl.ucl.ac.uk /www_astro/agn/agn_beginners.html (292 words)

	Active Galactic Nuclei (Site not responding. Last check: 2007-11-01)
		We find little evidence for an increase in the fraction of AGN in the sample as a function of far-IR luminosity but our sample covers only a small range in infrared luminosity and thus a weak trend may be masked.
		It is suggested that the AGN phase corresponds to the early-type phases of galaxies.
		The active nuclear engines of non-HBLR S2s then, appear to be truly weaker than HBLR S2s, which in turn, are fully consistent with being S1s viewed from another direction.
	www.noao.edu /staff/morrison/home/notes/AGN.html (1217 words)

	Linné on line - Active Galactic Nuclei
		Galaxies with active nuclei are similar to spiral galaxies.
		The amount of energy that is converted in active galactic nuclei is enormous.
		This active galactic nucleus has also been observed by the Hubble space telescope.
	www.linnaeus.uu.se /online/phy/macrocosmos/agn.html (214 words)

	Study supports theory of quasars
		Since the early 1980s, the most widely accepted model of AGNs, called the unified theory, involves a basic structure: a fl hole at the center, an accretion disc (a round, flat sheet of gas) around it and a doughnut-shaped ring of dusty gas, called a torus, around the accretion disc.
		The model holds that all AGNs share the same fundamental characteristics, but it allows for different radiation patterns with the premise that how an AGN looks depends on the perspective of the observer.
		AGNs include quasars, which look like stars in optical telescopes but emit massive amounts of radiation; Seyfert galaxies, low-energy counterparts of quasars; and blazars, which are AGNs viewed pole-on and which show rapid variations in radiation output over short intervals.
	www.news.cornell.edu /stories/June05/spitzer.quasars.hao.lg.html (704 words)

	AGN
		Active galactic nuclei (AGN) are galaxies that have very energetic central regions, due to either the presence of a fl hole or star formation activity at the core of the galaxy.
		Three main types of AGN are quasars, ("quasi-stellar objects" or QSOs), which are very compact objects that resemble stars in optical images; Seyfert galaxies, characterized by fluctuations in brightness at their cores; and radio galaxies, which emit massive jets of gas powered by fl holes at their cores.
		Other images of AGN can be found in the VLBA 2cm Survey of Compact Radio Sources and the Jodrell Bank Atlas of DRAGNs.
	www.nrao.edu /imagegallery/php/level2.php?class=AGN (289 words)

	Active galactic nuclei books, find the lowest prices
		AGN Surveys : IAU Colloquium 184 Proceedings of a Colloquium Held at Byurakan, the Republic of Armenia, 18-22 June, 2001
		Mass Outflow in Active Galactic Nuclei : New Perspectives Proceedings of the Workshop on Mass Outflow in Active Galactic Nuclei, 2001 Washington, D. by D.
		Relationships Between Active Galactic Nuclei and Starburst Galaxies : Proceedings of the Taipei Astrophysics Workshop, Academia Sinica, Taipei, Taiwan, Republic of China, 25-30 March 1991
	www.allbookstores.com /Active_Galactic_Nuclei_st.html (411 words)

	Active Galactic Nuclei
		Quasars are very distant AGN - the most distant quasars mark an epoch when the universe was less than a billion years old and a sixth of its current size.
		In some cases, the size of the AGN is smaller than the size of our solar system.
		Based on X-ray (and other) observations, a good guess is that the power source in AGN is a supermassive fl hole.
	heasarc.gsfc.nasa.gov /docs/objects/agn/agntext.html (225 words)

	Astronomy and cosmology: Active galactic nuclei
		The x-ray space observatory XMM-Newton is currently the most efficient AGN-detector in operation, and expects to be able to survey AGN back to a time when the Universe was only about a billion years old - making them important probes of the very early Universe.
		One of the objectives of the European Space Agency's gamma-ray observatory INTEGRAL is to study gamma-rays coming from the centre of our own Galaxy which may confirm earlier reports from the American Chandra X-ray observatory that there is a giant fl hole lurking there.
		Active galaxies were first discovered in the 1960s from their radiowave emission (they actually emit at all wavelengths).
	www.pparc.ac.uk /Ps/aac/aac_vuniv_an.asp (270 words)

	X-ray AGN Intro (Site not responding. Last check: 2007-11-01)
		Perhaps the most popularly known instance of AGN are "quasars" which are AGN that are very distant, up to 60 billion light years away.
		Based on X-ray, radio, and other observations, a good guess is that the power source in AGN is a supermassive flhole.
		Many AGN also show evidence for a huge torus of gas around the flhole.
	aether.lbl.gov /www/projects/neutrino/agn/agn.html (286 words)

	Amazon.com: Active Galactic Nuclei (Princeton Series in Astrophysics): Books: Julian H. Krolik (Site not responding. Last check: 2007-11-01)
		Astrophysics Of Gaseous Nebulae And Active Galactic Nuclei by Donald E. Osterbrock
		Active galactic nuclei (hereafter abbreviated "AGNs") are among the most spectacular objects in the sky.
		Active galactic nuclei (Saas-Fee advanced course 20 lecture notes) by Roger D Blandford in Back Matter
	www.amazon.com /Active-Galactic-Nuclei-Princeton-Astrophysics/dp/0691011516 (1021 words)

	Active galactic nuclei (Site not responding. Last check: 2007-11-01)
		Active galactic nuclei (AGN) are powerful sources of radiation which exist in the centre of 1-10 per cent of all galaxies.
		Galaxies which host an AGN are known as active galaxies.
		As discussed below, it is now widely believed that AGN are powered by the disk-accretion of material onto a supermassive fl hole at the centre of the active galaxy.
	www.astro.umd.edu /~chris/publications/thesis/node2.html (224 words)

	Exotic Galaxies and Active Galactic Nuclei (Site not responding. Last check: 2007-11-01)
		Radio, infrared, optical emission line and X-ray observations are all being obtained and used in modelling the nuclei and environments of radiogalaxies and quasars.
		All of these techniques are being applied to recently discovered young objects at high redshift, which allow direct study of active galaxies forming early in the Universe.
		Dense star clusters, molecular clouds, a rotating disk and perhaps a fl hole and jets are all to be found there: using radio and millimetre-wave telescopes, we are studying these exotic phenomena in an attempt to understand the underlying physical processes taking place both at the centre of our own and of other galaxies.
	www.mrao.cam.ac.uk /research/AGN.html (299 words)

	ScienceDaily: Astronomer Brings Coherence To Study Of Active Galactic Nuclei
		The book, "Active Galactic Nuclei: From Central Black Hole to the Galactic Environment," published by Princeton University Press, is being touted by one of the world's leading astronomers, Sir Martin Rees, as "an impressive book (that) fills a notable gap in the existing literature."
		Because what really distinguishes AGN is that they emit enormous amounts of power across the spectrum, all the way from radio wavelengths to X-rays, and sometimes even high-energy gamma-rays.
		It is estimated today that as many as one in five of all research astronomers are making inquiries into AGN or some aspect of their awesome components.
	www.sciencedaily.com /releases/1999/03/990305141152.htm (1936 words)

	Galaxies and Active Galactic Nuclei
		This soft component is present in two Galactic LMXBs which lie in directions of low Galactic hydrogen column densities, and in LMXBs in the bulge of M31, which comprise a majority of the X-ray emission in the bulge of that galaxy.
		C.-Y. Wang (graduate student) and Sarazin are analyzing the ROSAT HRI observation of the elliptical galaxy NGC 1404 in the Fornax cluster.
		Whittle has continued a study of gas kinematics in galactic nuclei, extending his earlier work on Seyfert nuclei to related nuclei of LINER galaxies and starburst galaxies.
	www.astro.virginia.edu /research/aas97/galaxy.html (2789 words)

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