Models of The Active Nucleus
For a long time it has been argued that AGN must be powered by accretion onto massive black holes (with masses between 106 and 1010 times that of the Sun). AGN are both compact and persistently extremely luminous; accretion can potentially give very efficient conversion of potential and kinetic energy to radiation, and a massive black hole has a high Eddington luminosity, so that it can provide the observed high persistent luminosity. Central supermassive black holes are now believed to exist in the centers of most or all massive galaxies: the mass of the black hole correlates well with the velocity dispersion of the galaxy bulge (the M-sigma relation) or with bulge luminosity (e.g.). Thus AGN-like characteristics are expected whenever a supply of material for accretion comes within the sphere of influence of the central black hole.
Read more about this topic: Active Galactic Nucleus
Famous quotes containing the words models of, models, active and/or nucleus:
“The parents who wish to lead a quiet life I would say: Tell your children that they are very naughty—much naughtier than most children; point to the young people of some acquaintances as models of perfection, and impress your own children with a deep sense of their own inferiority. You carry so many more guns than they do that they cannot fight you. This is called moral influence and it will enable you to bounce them as much as you please.”
—Samuel Butler (1835–1902)
“French rhetorical models are too narrow for the English tradition. Most pernicious of French imports is the notion that there is no person behind a text. Is there anything more affected, aggressive, and relentlessly concrete than a Parisan intellectual behind his/her turgid text? The Parisian is a provincial when he pretends to speak for the universe.”
—Camille Paglia (b. 1947)
“There is not enough exercise in this way of life. I try to make up by active gymnastics before I dress when I get up, by walking rapidly in the lower hall and the greenhouse after each meal for perhaps five to ten minutes, and a good hand rubbing before going to bed. I eat moderately; drink one cup of coffee at breakfast and one cup of tea at lunch and no other stimulant. My health is now, and usually, excellent.”
—Rutherford Birchard Hayes (1822–1893)
“I could not undertake to form a nucleus of an institution for the development of infant minds, where none already existed. It would be too cruel.”
—Henry David Thoreau (1817–1862)