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Topic: Active galaxies


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In the News (Wed 19 Jun 19)

  
  Active Galaxies and Quasars - Introduction
Active galaxies are galaxies which have a small core of emission embedded in an otherwise typical galaxy.
Models of active galaxies concentrate on the possibility of a supermassive fl hole which lies at the center of the galaxy.
Active galaxies are intensely studied at all wavelengths.
imagine.gsfc.nasa.gov /docs/science/know_l1/active_galaxies.html   (1211 words)

  
 Seyfert Galaxies & Active Galaxies
The nuclear regions are so luminous that they account for much of the galaxy's light, often having the appearance of stars in photographic plates because they so strongly outshine their spiral host galaxies [Seyfert, 1943].
The defining characteristic of active galaxies is the presence of an extremely energetic process in their nuclei.
Their radio emissions can be so powerful that the brightest objects in the radio sky are active galaxies, despite the fact that they are also some of the farthest objects known.
taltos.pha.jhu.edu /~jonathan/papers/proposal/node1.html   (406 words)

  
 Galaxies
Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars, of masses between several million and several trillion times that of our Sun, of an extension of a few thousands to several 100,000s light years, typically separated by millions of light years distance.
The most massive galaxies are giants which are a million times more massive than the lightest: Their mass range is from at most some million times that of our Sun in case of the smallest dwarfs, to several trillion solar masses in case of giants like M87 or M77.
Among the biggest Messier galaxies are the Andromeda galaxy M31 and the bright active Seyfert II galaxy M77.
www.seds.org /messier/galaxy.html   (2049 words)

  
 Active galaxies Congresses. - Astronomy - What's Been Published
Active galactic nuclei : proceedings of a conference held at the Georgia State University, Atlanta, Georgia, October 28-30, 1987 / H. Richard Miller, Paul J. Wiita, eds.
Active galactic nuclei : proceedings of the 134th Symposium of the International Astronomical Union, held in Santa Cruz, California, August 15-19, 1988 / edited by Donald E. Osterbrock and Joseph S. Miller.
Variability of active galaxies : proceedings of a workshop of the Sonderforschungsbereich 328, held at Heidelberg, Germany, 3-5 September 1990 / W.J. Duschl, S.J. Wagner, M. Camenzind, eds.
www.pitbossannie.com /rps-qb-active-galaxies-congresses.html   (522 words)

  
 Space News - active galactic nuclei (AGN) galaxies quasars - January 2005   (Site not responding. Last check: 2007-09-07)
Active Galactic Nuclei (AGN) are known to release vast amounts of energy sometimes outshining all the other stars in a galaxy combined but their role in affecting their surroundings is only now being discovered.
Coincident with the active nucleus itself is a compact radio core and emanating from this core are enormous jets of plasma, fully ionised matter, moving at close to light speed.
The evolution of elliptical galaxies and spheroids of spirals display family traits that are, said Ostriker, best understood in terms of a period of star formation, followed by the loss from the system of the remaining primordial gas and the reprocessed gas from dying stars.
www.sciencebase.com /active_galaxies_quasars.html   (5164 words)

  
 ADC Quick Reference: Basic Data on Groups and Clusters of Galaxies   (Site not responding. Last check: 2007-09-07)
7004A Abell and Zwicky Clusters of Galaxies (Abell+ 1974)
J/AJ/106/1273 The kinematics of dense clusters of galaxies.
J/A+A/303/661 Star-forming galaxies in the Coma Cluster (Donas+, 1995)
adc.gsfc.nasa.gov /adc/quick_ref/ref_clusters.html   (1447 words)

  
 Active Galaxies
Generally, active galaxies have spectra that look rather different from that to be expected from a collection of billions of stars, as illustrated in the top right figure.
The nonthermal emission from these galaxies is largely associated with synchrotron radiation, which is illustrated in the above figure and in this animation.
Although in many cases the classes of active galaxies were originally thought to be distinct, the modern view is that the different classes of active galaxies are related phenomena, and that they all may be powered by rotating, supermassive fl holes at their centers.
csep10.phys.utk.edu /astr162/lect/active/active.html   (229 words)

  
 Active galaxies and black holes
These "active galaxies" are believed to be powered by the appetite of massive fl holes in their centers, which gobble up matter through their relentless gravitational pull and transfer mass to energy in the process.
The radio emission of the active galaxies was puzzling because it could not be attributed to a collection of stars and gas under normal conditions.
Active galaxies turned out to be among the brightest sources of X-ray emission in the sky.
www-int.stsci.edu /~marel/abstracts/abs_L2.html   (1794 words)

  
 Spitzer Science: Galaxies
An active galaxy is characterized by extremely intense non-thermal emission, typically at radio and x-ray wavelengths, the signature that a high-energy process is at the core of the intense radiation (the active galactic nuclei, or AGN).
Starburst galaxies exhibit unusually high rates of star formation on large scales, and are therefore dominated by infrared and visible-light emission from young and massive stars.
Galaxies are often found in large gravitationally bound clusters that are many times larger than their analogous stellar cousins.
sirtf.caltech.edu /science/galaxies/index.shtml   (758 words)

  
 Active Galaxies
The term "active galaxy" refers to a galaxy that shows a huge internal production of energy, which is usually located in its nuclear region.
Active galaxies are divided in several classes, according to their appearance, to the amount of emitted energy and to their spectrum.
Active galaxies are often strong sources in "unusual" spectral bands, that is the radio and X bands.
www.pd.astro.it /E-MOSTRA/NEW/A5020ATT.HTM   (1311 words)

  
 Active Galaxies - Zoom Astronomy
An active galaxy is a galaxy (a huge group of stars, dust, gas, and other celestial bodies bound together by gravitational forces) that produces huge amounts of energy; they produce more energy than the total energy emitted from each of the stars in the nebula.
There may be at least three types of active galaxies, including Seyfert galaxies, quasars, and blazars (although they may be the same type of galaxy view from different distances and perspectives).
Active galactic nuclei are galaxies that have a massive fl hole at the galactic center (nucleus).
www.enchantedlearning.com /subjects/astronomy/stars/galaxy/active.shtml   (331 words)

  
 Active Galaxies   (Site not responding. Last check: 2007-09-07)
Observations of M87 suggest that the cores of these galaxies are extremely crowded and that the stars near the core are moving very rapidly.
The lobes of radio galaxies are simply the jets produced by the heated accretion disk, and quasars are extremely bright because they are the cores of galaxies which have extremely massive fl holes at their centers.
Some astronomers believe that active galaxies are bright because they have extensive star formation occuring at their centers.
www.astro.umd.edu /education/astro/actgal/actgal.html   (619 words)

  
 Active Galaxies
Radio galaxies, quasars, and blazars are AGN with strong jets, which can travel outward into large regions of intergalactic space.
The radio components include: the compact core at the galaxy nucleus, jets, lobes, and a hot spot where the jet slams into the interstellar medium.
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)

  
 Active Galaxies Educator Unit
In sum, the basic components of an active galaxy are: a supermassive fl hole core, an accretion disk surrounding it, and a torus of gas and dust, and in some (but not all!) highly focused jets of matter and energy.
Galaxies are a fundamental structure in the Universe, and the supermassive fl holes in their nuclei are in turn a fundamental part of galaxies.
Active galaxies are a fundamental part of the evolutionary process of the universe.
www-glast.sonoma.edu /teachers/agn/index.html   (7871 words)

  
 Active Galaxies   (Site not responding. Last check: 2007-09-07)
Some galaxies are classified as active galaxies because of the extraordinary variability and evidence of strong interactions in their galactic nuclei.
Compared to ordinary galaxies, some galactic nuclei have extraordinary luminosities and are called active galaxies.
One class of active galaxies is the Seyfert galaxies.
hyperphysics.phy-astr.gsu.edu /hbase/Astro/actgal.html   (117 words)

  
 The Hosts of Active Galaxies   (Site not responding. Last check: 2007-09-07)
The failure to find evidence for bars in most Seyfert galaxies may be due to the fact that early studies concentrated on optical wavelengths where the presence of extinction or a young stellar population might mask any bar structures.
For example, the prototypical Seyfert 2 galaxy NGC 1068 is classified as an unbarred spiral at optical wavelengths, but a strong bar is clearly seen in near-infrared images.
The near-infrared is expected to be a good place to study the host galaxy of Seyferts because the galaxy energy distribution peaks at approximately 1 micron, while the energy distribution of the active nucleus is at a minimum here.
www.ociw.edu /%7Emulchaey/nearir.html   (729 words)

  
 New Type of Black Hole May Turn Starburst Galaxies Inside Out   (Site not responding. Last check: 2007-09-07)
Starburst galaxies -- those distant gems set aglow in a colorful lifecycle of star birth, death and renewal -- may be the stepping stone to a far brighter phenomenon: a quasar-type galaxy with a supermassive fl hole at its core.
Starburst galaxies are known for their brightness caused by a high concentration of young, massive stars and supernova explosions.
The bulk of a starburst galaxy's luminosity is from outside of the core region.
www.gsfc.nasa.gov /gsfc/spacesci/chandra/starburst.htm   (854 words)

  
 CERN Courier - Looking deep into galaxies - IOP Publishing - article
Dayton Jones of Caltech presented a radio image of the centre of galaxy NGC6241, showing two jets projecting outwards from the centre, as is common in such active galaxies.
Radio observations of gas movement in the centres of galaxies and spectral line data from the HST suggest that super-massive fl holes exist in the centre of every galaxy.
Observations of the antennae galaxies, colliding galaxies with streams of material emanating from their core, reveal huge bubbles of hot gas at X-ray wavelengths, and provide an example of conditions when our universe was young and galaxies were forming.
www.cerncourier.com /main/article/40/9/13   (1547 words)

  
 Active Galaxies and Quasars
Photographs of a Seyfert galaxy (NGC 5728) from the ground and from Earth orbit.
The red dot at left marks the bright nucleus of the galaxy; the red and yellow blob near the center of the image corresponds to the bright "knot" visible in the jet in (b)
When light from a distant object passes close to a galaxy or cluster of galaxies along the line of sight, the image of the background object (here, the quasar) can sometimes be split into two or more separate images
physics.uoregon.edu /~jimbrau/astr123/Notes/Chapter25.html   (1864 words)

  
 Active Galaxies and Quasars   (Site not responding. Last check: 2007-09-07)
It is widely believed today that quasars and active galaxies are powered by supermassive fl holes which produce copious luminosity even as they gobble their prey.
For instance, some Seyfert galaxies show evidence for cones of radiation which are thought to be collimated by an opaque torus of cool gas that surrounds the fl hole and the accretion disk.
This galaxy will be re-observed on Astro-2, using multiple pointings spread through the mission to study the variability of the UV emission on timescales of days to weeks.
praxis.pha.jhu.edu /astro2/astro2_science/agq.html   (1013 words)

  
 Gene Smith's Astronomy Tutorial - Active Galaxies
This was a surprise because galaxies had been thought to be collections of billions of stars along with bits of hydrogen gas and dust.
Seyfert galaxies are divided into two classes, based upon the widths of their spectral emission features.
The Seyfert 1 galaxy above has hydrogen emission features with very large widths, indicating that the gas in the galaxy's central regions is moving with velocities of several thousand km/sec (Seyfert 1 galaxies show velocities up to almost 0.1c).
cassfos02.ucsd.edu /public/tutorial/AGN.html   (914 words)

  
 John Kormendy: Search for Supermassive Black Holes in Galaxy Nuclei   (Site not responding. Last check: 2007-09-07)
Active nuclei range from faint, compact radio sources like that in M31 to quasars like 3C 273 that are brighter than the whole galaxy in which they live.
Blue points are based on the motions of stars; green points are based on the motions of hot gas, and red points are based on the motions of cold gas in which water molecules emit maser radiation.
How fast the stars move is determined by how much the galaxy collapsed inside its dark matter halo before stars formed.
chandra.as.utexas.edu /~kormendy/bhsearch.html   (684 words)

  
 New Scientist Breaking News - 'Red and dead' galaxies surprise astronomers
The corpses of three "dead" galaxies - which to the surprise of astronomers stopped forming stars long ago - have been identified by the Spitzer Space Telescope during a survey of the distant, early universe.
The galaxies appear to be as massive as the Milky Way and like our galaxy, may harbour "supermassive" fl holes containing the mass of millions of Suns.
This enormous energy is thought to heat the gas remaining throughout the galaxy to tens of millions of degrees.
www.newscientist.com /article.ns?id=dn7132   (592 words)

  
 Jodrell Bank - Microquasars, Quasars & Radio Galaxies   (Site not responding. Last check: 2007-09-07)
Super-massive fl holes at the heart of galaxies with a mass of up to a billion suns appear to be the cause of the most energetic sources of emission in the Universe.
The centres of such galaxies are called Active Galactic Nuclei and when they emit a beam of radiation that points towards us, the intense, often point like objects that we observe are called Quasars.
Micro-quasars are objects in our own galaxy which also contain fl holes, but here the fl hole results from the collapse of the core of a massive star at the end of its life.
www.jb.man.ac.uk /booklet/Quasars.html   (432 words)

  
 A - Astronomy Glossary: Absolute magnitude, Accretion disc, Active galaxies...
Active galaxies: Galaxies that release huge amounts of energy, mostly long-wavelength radiation, such as radio waves.
A common type of active galaxies are Seyfert galaxies.
Aphelion: The point in a planet's orbit around the sun on which it is furthest.
www.novacelestia.com /glossary/a.html   (358 words)

  
 RAS Press Notices   (Site not responding. Last check: 2007-09-07)
As the gas gets closer to the fl hole, more and more energy is released in the form of light and other electromagnetic radiation, including X-rays originating close to the fl hole where the gas is hottest.
Galaxies where this process is taking place are called 'active' galaxies.
Dr Uttley explains: 'The X-ray variations of active galaxies and BHXRBs can be likened to music, showing small variations - single notes - on short time-scales, and larger variations - whole key changes - on longer time-scales.
www.ras.org.uk /html/press/pn02-09.htm   (424 words)

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