Transcript Chapter 25 Active Galaxies and Quasars

Chapter 25 Active Galaxies and
Quasars
• Active galaxies are galaxies which are
much more luminous than normal galaxies
and have spectra that are nonstellar in
nature.
•This indicates that the energy they
emit is not simply the accumulated
light of many stars.
•Most of the energy from active
galaxies is in the radio and infrared
portions of the spectrum.
Planck curves for Active and Normal
Galaxies
Seyfert Galaxies
• Look like normal spiral galaxies except
with extremely bright central galactic
nucleus.
•The luminosity of the nucleus can
exceed that of the rest of the galaxy.
•Spectral lines are very broad,
indicating rapid rotation.
•Luminosities can vary by large
amounts in fractions of a year.
Irregular variation of Seyfert
galaxy luminosity “3C 94”
Radio Galaxies
• Active galaxies that emit most of their
energy in the radio part of the spectrum.
•Comparable to Seyferts in total
energy output.
•Usually associated with
elliptical galaxies.
Two Types Of Radio Galaxy
• Core- Halo Radio Galaxy: Energy is
emitted from a small central nucleus, as
with a Sayfert Galaxy.
•Lobe Radio Galaxy: Energy is emitted
from enormous radio lobes. These lobes
usually lie far beyond the galactic
nucleus and are usually much larger
than the visible part of the galaxy.
Radio contour of typical corehalo Radio galaxy
M87 At Different Wavelengths
Typical Lobe Radio Galaxy “Centaurus A”
Difference between halo and lobe
radio galaxies may just be a
matter of perspective
Central energy source producing
high-speed jets of matter may
appear to us as either a lobe or
core halo radio galaxy,
depending on our location with
respect to the jets and lobes.
Core-Halo & Lobe Radio Galaxy
Active Galaxies show some or all
of the following properties.
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High Luminosities.
Energy emission is nonstellar.
Energy output can be highly variable.
Often exhibit “jets” and other signs of
explosive activity.
• Spectra show broad emission lines indicate rapid internal motions.
Central Engine of Active Galaxy
NGC 1461 in Virgo Cluster
M87 - Virgo Cluster
Energy Emission
• Although the rotating supermassive black
hole model is now widely accepetd, the
actual mechanism for the energy production
is uncertain.
• One popular model which explains some
features is the synchrotron radiation model.
Synchrotron Radiation
• A type of nonthermal radiation produced by
high-speed charged particles, such as
electrons, as they are accelerated in a strong
magnetic field.
Synchrotron Radiation
Quasi-stellar Objects (QUASARS)
• Circa 1960, astronomers observe what
appear to be faint blue stars identified with
radio sources.
• These objects had odd spectral lines which
appeared broadened and extremely
redshifted.
Early quasars
3C 275
Field of quasars
QSO 1229+204
Optical Spectra of 3C 273
Some Quasars also have jets (3C 273)
Quasar 2300-189
• Quasars are :
• believed to be some of the oldest
objects in the universe.
• some of the most distant objects
from us.
• the most luminous objects known.
Quasar Mirages - AC114
Example of gravitational lensing
Gravitational lens
Active Galaxy Formation
• Possible evolutionary track for
galaxies may be as follows:
–Quasars --->
–Radio/Sayfert Galaxies --->
–Normal spiral and elliptical
galaxies.
• Black holes are always present, but
reduce over time as they run out of
fuel.
End Section and Ch 25
Final Exam- Spring 2002
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