The Unified Model of Quasi-Stellar Objects

Dr. Christopher Sirola

Department of Physics & Astronomy

University of Southern Mississippi

Finding quasars just by looking is like finding a renegade Roman gladiator…

I am Spartacus!

I am Spartacus!

I am Spartacus!

Can you identify the

quasar in this picture?

Here!

attempts in vain to deduce the identity of .

                                     attempts to determine is, but the prisoners will

not identify him.  Many make the claim of "I am!".  As punishment the survivors are crucified on the road to Rome. In reality, 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."

A Brief History of Quasars

The First Quasar – 3C 273– Cyril Hazard used occultation of the

Moon to identify radio emission with 3C 273

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 abrupt disappearance of the radio emission from 3C 273 allowed Hazard to identify its optical counterpart.

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

Wavelength (angstroms)

This peak is a redshifted Hydrogen alpha emission line.

Note the flat “base” of the

spectrum with various

emission peaks.Si IV C IV

The Unified ModelThe 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

Overlapping optical & radio maps of NGC 4261

Accretion disk

Black Hole inside here

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

QSOs are ancient objects and tend to

have high metal abundances. How?

Silicon

Carbon

Nitrogen

M82 – an example of a starburst galaxy.

When galaxies collide, gas is mixed & compressed, spurring explosive rates of star formation and subsequent supernovae.

The same goes for QSOs.

Other Studies of QSOsQSOs 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

Component B

Lensing galaxy

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).

Component A is in blue

Component B is in red

Future questions regarding QSOs•o    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)

 •o    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%)

 •o    Geometry of BALR       - Torus? - Spherically symmetric? - Special class?

(addressed by my work but results were inconclusive)

Thanks for your attention!