Transcript The Unified Model of Quasi

The Unified Model of
Quasi-Stellar Objects
Dr. Christopher Sirola
Department of Physics & Astronomy
University of Southern Mississippi
I am Spartacus!
I am Spartacus!
I am Spartacus!
Finding quasars just by looking is like finding
a renegade Roman gladiator…
Can you
identify the
quasar in this
picture?
Here!
A Brief History of Quasars
attempts in vain to deduce the identity of
The First Quasar – 3C 273
– Cyril Hazard used
occultation
attempts
to determineof
is,the
but the
Moon to identify radio emission with
prisoners will not identify him. Many make the claim of "I am!". As
273 are crucified on the road to Rome. In reality,
punishment3C
the survivors
.
6,000 were nailed up along the road, but has him killed in the battle. "And
so making directly towards himself, through the midst of arms and wounds, he missed him, but slew two centurions that fell upon him
together. At last being deserted by those that were about him, he himself stood his ground, and, surrounded by the enemy, bravely
defending himself, was cut in pieces."
The abrupt
disappearance of the
radio emission from
3C 273 allowed
Hazard to identify its
optical counterpart.
If the source is large,
its light should gradually
decrease as the Moon
covers it. If it is a point
source, its light should
disappear abruptly.
The First Quasar – 3C 273
– Maarten Schmidt then discovered
unknown emission lines in the
spectrum of 3C 273 were actually
Balmer hydrogen lines, but redshifted.
General properties of QSOs
• Names
- “Quasar” = “quasi-stellar radio source”
- “QSO” = “quasi-stellar object”
- The difference is the presence or lack of radio
emission
• Location
- Objects are extragalactic
- Objects show enormous redshifts
- Objects must be extremely far away
- Objects also seen from extremely distant past
- Associated with cores of galaxies
An HST QSO Portrait Gallery
Photometric properties
• Only  10% are bright radio emitters
(“true” quasars)
• Extremely bright (tens to thousands
of times brighter than typical galaxies)
• Highly variable
– Outputs can rise or fall by several
magnitudes
– Outputs can change over very short
periods of time (even as short as hours;
also days, weeks, months, & years)
Spectral properties
• Have large redshifts (NO blueshifts!)
• Base of spectrum is flat
– Implies energy emitted at variety of
wavelengths
• Usually have broad emission lines
– Implies high velocities of emission region
• ~ 10% have broad absorption lines
• Many elements besides H & He:
– C, N, O, Si, Fe, etc.
– Implies copious star formation
A Sample Spectrum of a QSO
Relative
flux
This peak is a
redshifted
Hydrogen alpha
emission line.
Si IV
C IV
Wavelength (angstroms)
Note the flat
“base” of the
spectrum
with various
emission
peaks.
The Unified Model
• QSOs belong to a larger population
of Active Galactic Nuclei (AGN)
• Supermassive Black Hole at Core
– Over 1 million solar masses
– Can get as high as  1 billion solar masses
Accretion disk rotates rapidly
around black hole
• May extend several tens of AU (few mpc)
• Gas heated by collisional excitation
• Gas is hotter going toward black hole
– Gives rise to flat spectrum
– Extends from radio to x-ray
• Black Hole + accretion disk referred to as
“Central Engine” (CE)
• Efficiency of energy production 10-20%
– Compare to H fusion (0.7%)
A model of a QSO (courtesy NASA)
HST Images of Black Holes
in the Cores of Galaxies
Black Hole
inside here
Accretion disk
Overlapping optical & radio maps of NGC 4261
Comparisons between galaxies & quasars:
Quasars typically overwhelm the light from
the rest of the galaxies they inhabit.
An optical image of a
Seyfert galaxy, an
intermediate type of
Active Galaxy that
appears in some
spirals.
Other regions surrounding the
Central Engine
• Broad Emission Line Region
• Clouds near the CE in rapid, random orbits
• Temperatures high enough for ultraviolet emission
• Broad Absorption Line Region
• Torus of thick gas surrounding CE and BEL region
• Temperatures low enough for absorption of UV
• Jets
• Synchrotron radiation from particles caught in magnetic
field of accretion disk
Another NASA
representation
of the Unified
Model.
Various Subsets of AGN
• Specific types depend on spectra
• Looking down on jets
• High & quick variability, washed-out spectral lines
• Blazars, BL Lac objects, Optically Violent Variables
• Looking through torus
• High polarization
• Quasars, Radio-lobe galaxies
• Looking between torus & jets
• Moderate variability
• QSOs, Seyfert galaxies
Locations of QSOs & AGNs
• Always seen in distant past
– QSO population peaks at redshift ~ 2
– Universe was ~ 7% of its current age
(i.e. ~ 1 billion years old)
• Now known to inhabit cores of ancient
galaxies
- Only 1 of every 1000 galaxies has a QSO
• If QSOs came to be in the distant past,
where are they now?
What fuels the black hole?
Black Holes are
often viewed as
oversize vacuum
cleaners.
• But black holes
don’t move freely
• Material
(gas & dust)
has to come
to the black hole
PKS 2349:
A collision between a
QSO and a galaxy.
The Central Engine
needs a supply of
material in order to
keep generating light.
Q1229+204
swallowing a
dwarf galaxy.
Black holes are (by definition!) invisible. We see them
only by their effects on their environments.
The Central Engine can last up to 500 million years
(0.5 billion years), a significant but small fraction
of the age of the Universe.
Primordial QSOs may have formed as early
as z  6 (about 9-10 billion years ago).
At left:
a painting of
a primordial
QSO.
Element abundances of QSOs
In general, most objects of the distant past
(Population II stars in the Milky Way, for
example) have low metal contents.
• Recall that “metals” for astronomers are elements
besides hydrogen and helium
Nitrogen
Silicon
Carbon
QSOs are ancient
objects and tend to
have high metal
abundances. How?
When galaxies
collide, gas is
mixed &
compressed,
spurring
explosive
rates of star
formation and
subsequent
supernovae.
The same
goes for
QSOs.
M82 – an example of a
starburst galaxy.
Other Studies of QSOs
QSOs can show up as gravitational lenses: intervening
galaxies warp space & we see multiple images of the QSO.
Above: The Einstein Cross.
Q0957+561 – the
first known QSO
gravitational lens.
Component A
Lensing
galaxy
Component B
Component A is in blue
Component B is in red
By comparing
the variations in
light from each
component of
Q0957+561, it is
possible to
estimate the
Hubble constant.
Results are
consistent with
other methods
(around 70
km/s/Mpc).
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Future questions regarding QSOs
Details regarding CE energy production
•- Including questions regarding variability
•- QSOs only vary  1/3 of the time
(result from my Ph.D. work; implications for
QSO search programs)
Development of supermassive black holes
- How do they form?
- Do the black holes come first or last?
- The “Maggorian Relation” – supermassive black hole
tends to be ~ 0.5% of total mass of host galaxy
(theory suggests ~ 0.1% to 0.2%)
Geometry of BALR
- Torus? - Spherically symmetric? - Special class?
(addressed by my work but results were inconclusive)
Thanks for your attention!