Quasars and Other Active GalaxiesQuasars and Other Active GalaxiesQuasars and Other Active GalaxiesQuasars and Other Active Galaxies

Active galaxies are brighter, and emit more non-stellar radiation

In this chapter you will discover… 5-10% of galaxies unusually bright, called active galaxies

The most distant objects we can see: quasars

Supermassive black holes are central engines for radio galaxies, quasars, Seyfert galaxies, & BL Lac objects

Distribution of Quasars is a key to the evolution of the Universe, and to the Big Bang Theory of its formation.

Active Galaxy TypesActive Galaxy Types

Seyfert GalaxiesSeyfert Galaxies: : Spirals with very bright centersSpirals with very bright centers

Radio GalaxiesRadio Galaxies: : Ellipticals with huge emissions of Ellipticals with huge emissions of radio energy in “lobes”radio energy in “lobes”

Quasars:Quasars: Very tiny, distant objectsVery tiny, distant objects

All have very bright, All have very bright, active galactic nucleiiactive galactic nucleii

Active Galactic NucleiActive Galactic Nuclei

• Seyfert GalaxiesSeyfert Galaxies

• spiral galaxies with spiral galaxies with incredibly bright, star-incredibly bright, star-like center (nucleus)like center (nucleus)

• they are very bright in they are very bright in the infraredthe infrared

• their spectra show their spectra show strong strong emissionemission lines lines

Circinus

Active Galactic NucleiActive Galactic Nuclei

• Seyfert GalaxiesSeyfert Galaxies

The luminosity can vary by as much as the entire brightness of the Milky Way Galaxy!!

Radio Galaxies

Cygnus A Radio Image

635 Million light years away, and still one of the brightest radio sources in the entire sky!

Active Galactic NucleiActive Galactic Nuclei Radio GalaxiesRadio Galaxies

||galaxies – usually giant galaxies – usually giant ellipticalsellipticals - which emit large amounts of radio waves - which emit large amounts of radio waves

the radio emission come from the radio emission come from lobeslobes on either side of the galaxy; on either side of the galaxy; notnot the the galaxy itselfgalaxy itself

Radio Galaxy LobesRadio Galaxy LobesThese lobes are swept back because the galaxy is moving through an intergalactic medium.

X-ray/Radio Image of Centaurus AX-ray/Radio Image of Centaurus A

X-ray is blue; radio is red

BL-Lac Objects

Superbright Elliptical Galaxy

Quasars

A peculiar Star-like object, emitting lots of radio waves? But not with a stellar spectral fingerprint!

Quasar SpectraQuasar Spectra

Star-like objectsStar-like objectsspectra that look spectra that look

nothing like a starnothing like a starFaint Hydrogen Faint Hydrogen

lines…lines…VERY red-shifted!VERY red-shifted!

Quasar ObservationsQuasar Observations

emit light at all wavelengthsemit light at all wavelengthsA hot dense source?A hot dense source?

occasionally VERY strong radio sourcesoccasionally VERY strong radio sourcesAssociated with jets from galaxies in clustersAssociated with jets from galaxies in clusters

Quasars Brightness varies in time!

Quasars Brightness varies in time!

QuasarsQuasars

Show enormous Show enormous redshiftsredshifts VERY far VERY far away by Hubble’s Lawaway by Hubble’s Law

Show extreme Show extreme variabilityvariability VERY small, VERY small, in scales of a light-hours to light years in scales of a light-hours to light years

….and so….….and so….

Quasars must be some of the most powerful Quasars must be some of the most powerful objects we know of in the universe!objects we know of in the universe!

Quasar DistributionQuasar Distribution

Seen at greatest distances Seen at greatest distances (earliest history of the universe!)(earliest history of the universe!)

Not seen nearby…. Not seen nearby….

But…But…

Quasar behavior in some nearer Quasar behavior in some nearer clustersclusters

AA theoretical model quasartheoretical model quasar

Must account for observations:Must account for observations:Small SizeSmall SizeEnormous energyEnormous energy output across spectrum output across spectrumSource of JetsSource of JetsSimilar behavior in Similar behavior in galaxies in clustersgalaxies in clustersSome radio synchrotron emission (indicating Some radio synchrotron emission (indicating

magnetic field)magnetic field)Full spectrumFull spectrum emission emission

A quasar model…A quasar model…

Supermassive Black Hole EngineSupermassive Black Hole Engine

Formed as Galaxies are born…Formed as Galaxies are born…

Pulling in gas, dust, and stars into huge Pulling in gas, dust, and stars into huge accretion diskaccretion disk

A quasar model…A quasar model…

Generating Generating jets of X-ray radiationjets of X-ray radiation for for millions of yearsmillions of years

““Quiet down” as fuel diminishesQuiet down” as fuel diminishes

““Re-ignited”Re-ignited” during collisions & mergers of during collisions & mergers of galaxies in clustersgalaxies in clusters

Quasar Energy Source?Quasar Energy Source? The energy is generated from matter falling onto The energy is generated from matter falling onto

a a supermassive black holesupermassive black hole…… 1.2 x 101.2 x 1099 M M for NGC 4261 for NGC 4261 3 x 103 x 1099 M M for M87 for M87

……which is at the center (nucleus) of the galaxy.which is at the center (nucleus) of the galaxy.

Quasar Energy Source?Quasar Energy Source?

Matter swirls through an accretion disk Matter swirls through an accretion disk before crossing over the event horizon.before crossing over the event horizon.

Gravitational energy lost like E = mcGravitational energy lost like E = mc22 • 10 – 40% of this is radiated away10 – 40% of this is radiated away

Process is very efficientProcess is very efficient

A quasar model…A quasar model…

Works to explain quasarsWorks to explain quasarsEven Supermassive Black holes are TINYEven Supermassive Black holes are TINYAccretion Disk generates thermal spectrum, Accretion Disk generates thermal spectrum,

jets, magnetic fieldsjets, magnetic fieldsHighly variable as mass is pulled inHighly variable as mass is pulled in

and…and…Works for active galaxies, too!Works for active galaxies, too!

Theory

Observation

Magnetic fields twistedMagnetic fields twisted

Pull charged particles out of disk & Pull charged particles out of disk & accelerate like slingshotaccelerate like slingshot

Particles bound to magnetic field; Particles bound to magnetic field; focused in a beamfocused in a beam

Quasar Jet Formation

Orientation determines what we see:Orientation determines what we see:

• if beams points at us, see a if beams points at us, see a quasarquasar

• if not, molecular clouds/dust of galaxy if not, molecular clouds/dust of galaxy block view of nucleusblock view of nucleus

• we see a radio galaxy or Seyfertwe see a radio galaxy or Seyfert

• lobeslobes are where jets impact are where jets impact intergalactic mediumintergalactic medium

Model Quasar Accounts for Other Observations, too

Hubble space telescope shows us that Hubble space telescope shows us that quasars do live in galaxies…they are quasars do live in galaxies…they are

Active Galactic Nuclei!Active Galactic Nuclei!

If the theory is right --- all galaxies start with Black Holes!

Evidence Quasars are distant?Evidence Quasars are distant?

Hubble’s LawHubble’s LawAssociation with Galaxies in clustersAssociation with Galaxies in clustersGravitational LensingGravitational Lensing

Essay Questions to Know!Essay Questions to Know!

What are active galaxies? How do active galaxies produce their energy? How do we know?

What are quasars, and where are they found? What do they tell us about the universe?