Download Quasars - Ann Arbor Earth Science

Active Galactic Nuclei
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The most distant and luminous objects in the known universe.
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A unique laboratory for the study of matter in extreme physical conditions.
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Now widely thought to be powered by accretion onto a supermassive black
hole
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Study of the central engines can shed light not only on the nature of the
AGN phenomenon, but also on the properties of black holes.
AGN have been historically identified and classified by their optical and ultraviolet
spectral features. However, it is becoming clearer that the most direct way of
investigating the fundamental energy source (the accretion flow onto the black
hole) is the study of the X-ray emission.
Active Galaxies bridge the
energy gap between ordinary
galaxies and quasars
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peculiar galaxies (pec)
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appear to be blowing themselves apart
Active Galaxies bridge the
energy gap between ordinary
galaxies and quasars
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peculiar galaxies (pec)
–
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appear to be blowing themselves apart
Seyfert galaxies
Seyfert galaxy - luminous, star-like nuclei with strong
emission lines. On closer inspection it is a galaxy,
usually a spiral or disturbed system, whose strong
emission lines are too broad and of ionization too high
to be produced by the galaxy's stellar population.
In type 1 Seyferts, some of the emission lines, those
that can be produced at high densities, are still broader,
while in type 2 nuclei, all the linewidths are comparable.
Seyfert nuclei are strong X-ray sources, and many show
significant radio emission.
BL Lacertae objects (BL Lacs)
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featureless spectrum with a brightness that
can vary by a factor of 15 times in a few
months.
BL Lacertae object - a variety of active galactic nucleus with a nearly featureless
spectrum and rapid strong variability. These may be other kinds of radio-loud AGN seen
nearly along their jets, so that the Doppler-boosted radiation from the jet overwhelms
everything else.
Blazar - broader term including BL Lacertae objects and those quasars which share
their characteristics of unusually weak spectral features, plus strong and rapid variability.
LINER - Low-Ionization Nuclear Emission-line Region, gaseous regions common in the
centers of many kinds of galaxies. 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.
Quasar - from QuasiStellar Radio Source, an object at
large redshift (z>0.1) showing strong broad emission
lines. Variability shows that the energy must arise in a
tiny region, although some quasars have hundreds of
time the energy output of normal galaxies. Their radio
structures often include jets and lobes similar to what
we see from radio galaxies.
Quasistellar object (QSO) - an object with optical
properties as described for quasars, but not necessarily
a strong radio source. Only about 10% of QSOs are
radio-loud. "Quasar" is often used more loosely to
include QSOs.
radio galaxy - a galaxy showing unusually strong radio
emission, too intense to be produced by the normal
processes of starbirth and stardeath. This may come
only from the nucleus, or from a pair of more or less
symmetric lobes stretching as far as a million light-years.
Many show emission from jets connecting the nucleus to
these lobes. Optical spectra of radio galaxies may show
nothing unusual, but in many instances show strong
emission lines, either narrow (NLRG, like type 2
Seyferts) or including broad lines of certain species
(BLRG, like quasars and type 1 Seyferts).
Radio image of Cygnus A showing a small but very
bright radio galaxy in the middle of the 320,000 ly
wide lobes
Active galaxies lie at the
center of double radio sources
superluminal sources - radio sources which show internal motions (for example,
increasing separation between the core and a knot in the jet) which appears faster than
the speed of light in our frame of reference. The data are consistent with this being a
transformation effect from seeing jets moving almost directly toward us, so that the
emitting material almost catches up with its own radiation. This has the effect of
compressing the scale of time that we measure for it, and so increasing the observed
speed.
Giant Gas
Clouds
(surrounding the
galaxy)
Intergalactic
gas jet
Galaxy
(which is actually
quite large)
The Discovery of Quasars (the first AGN
found)
Cyril Hazard – the
REAL DEAL
Maartin Schmidt – the ‘discoverer
of quasars’
The Cambridge Catalog of Radio
Sources
A few hundred of the brightest radio
sources were compiled with a radio
interferometer at Cambridge, England.
Unfortunately, the positions were not
accurately known. These were the
brightest radio sources in the sky – with
the exception of the Sun and planets…
The brightest was called 3C273.
3C273 could
be
anywhere in
this circle!
We needed
a better
position
Lunar Occultation
to the rescue!
Must get both entry
and exit from the
moons limb!!
The Parkes Radio Telescope
3C273
Radio (VLA)
X-ray
Schmidt measured the spectrum:
Redshift of 0.13 indicating that the object is very far away (about 2.5
billion light years) and very bright!
This object
that looks
like a star
must be
enormously
luminous its redshift
indicates it
is 4 billion
light years
Quasars and Seyfert I’s
Seyfert II’s
OΙΙΙ [5007] (forbidden)
OΙΙΙ [4959] (forbidden)
Hβ (permitted)
Quasars look like stars but
have huge redshifts
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object with a spectrum much like a dim
star
highly red shifted
enormous recessional velocity
huge distance (ala Hubble’s Law)
must be enormously bright to be visible
at such a great distance
Quasi-stellar object
QSO or Quasar
A quasar emits a huge amount of
energy from a small volume
Such rapid changes in brightness can only
result from changes in small objects
Supermassive black holes may lurk
at the centers of some galaxies
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High resolution spectroscopy allows
astronomers to peak at the motion of
gas near centers of galaxies
Some galaxies exhibit high-velocity
jets of material leaving the center
Observations suggest that the centers
of some galaxies are incredibly
massive
All of this suggests the existence of
supermassive black holes
Jets of matter ejected from around a black hole
may explain quasars and active galaxies
Jet
Narrow line region clouds
10 – 10000 ly
Broad Line Region
(Light months)
Dusty Molecular torus
10 – 1000 ly
Accretion Disk (light days)
Black Hole
100 million
solar masses
Narrow line region clouds
10 – 10000 ly
Broad Line Region
(Light months)
Dusty Molecular torus
10 – 1000 ly
Accretion Disk (light days)
Black Hole
100 million
solar masses
Gas and dust inhibit the jet
of particles!
Spiral versus Elliptical
galaxies
Blazar (BL Lac type)
CD Quasar
LD Quasar
BLRG
NLRG
Elliptical Galaxy
BAL QSO
QSO (SEYFERT I)
FIR GALAXY (SEYFERT II)
Spiral Galaxy
What should you know?
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What is the diameter
of the disk of the
Milky Way? Its disk
thickness?
Know how to compute
an escape velocity
(like the homework)
How do we know
what we know about
our Galaxy?
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What is a rotation
curve?
What is the major
difference between an
elliptical galaxy and a
spiral galaxy?
Who discovered Quasars?
How do we “see” black holes?
Jet
AGN
Narrow line region clouds
Model
10 – 10000 ly
Broad Line Region
(Light months)
Dusty Molecular torus
10 – 1000 ly
Accretion Disk (light days)
Black Hole
100 million
solar masses