AGN: Quasars
By:
Jay Hooper
Outline
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Types of AGN
Components of AGN
Differences between AGN
General Overview
Types of AGN
• AGN – Active
Galactic Nuclei
– Quasars
• QUAsi-StellAr
Radio source
– Blazars
– Seyfert
• Type 1
• Type 2
• Are thought to
be the same
objects viewed
in different
orientations
Components of AGN
• Supermassive black hole: 108 - 109 solar masses
• Broad-line region: dense clouds of ionized and
heated gas, by ultraviolet and x-ray photons,
rotating a velocities of 1000’s of km/s
• Accretion disk: Matter ripped apart by tidal
forces spiraling inward. Approx.
consumption of one solar mass of matter per
year is required to power a quasar
• Torus: doughnut-shaped region of molecular gas
and dust which is heated by the central source,
emitting infrared light, but which obscures the
central black hole, disk and broad-line region from
observers viewing the quasar edge-on.
• Narrow-line region: cone-shaped region of
illuminated clouds
• Jets: Oppositely-directed streams of plasma
thought to be discharged due to the winding up of
magnetic fields in an accretion disk that forms
around a massive black hole converting
gravitational and rotational energy into bulk
outflows at high speeds perpendicular to the disk.
Differences between AGN
• Quasars
– A clear view of the central
engine source.
– High-energy gamma-rays.
Usually 100 MeV or more,
even up to the GeV range
– Produces more light and
energy comparable to 101000 galaxies,in a region as
big as our solar system
• Blazars
– believed to be a quasar which has one of its relativistic
jets pointed directly toward the Earth. Therefore not as
luminous as quasars.
– Same energy levels as a quasar, but have been recorded
in the TeV range!
• Seyfert – two types divided by their spectral
emission features. Emitters of low energy gammarays on the order of 100KeV. Produce on the order
of .1 to 10 times the light and energy of our galaxy
• Type 1
– Has a hydrogen emission feature with very
large widths. Due to tilted jet angle.
• Type 2
– Has a hydrogen emission feature with much
narrower widths. AGN viewed edge on.
General Overview
Distances are computed
by their apparent redshifts, with the farthest
recorded z=5.5
corresponding to about
14 billion ly
– This is roughly a time
period when the
universe was 1/10 its
present age
• Give off radiation in the form of all
wavelengths
– Only about 10% are strong radio sources. The
rest are radio quiet.
• Size of source determined by time in
variation of intensity
– if an object varies significantly in brightness
over a period of a week, it cannot be larger than
a light-week in size.
• Superluminal motion
up to 10c.
– bursts of synchrotron
plasma shot out almost,
but not quite, toward
us at near speeds of c.
References
• http://skyandtelescope.com/news/article_964_1.asp
• http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.ht
ml
• http://www.cv.nrao.edu/~abridle/dragnparts.htm
• http://cassfos02.ucsd.edu/public/tutorial/AGN.html