Active GalaxiesA2290-35 1Powering “Active” GalaxiesRelativity and AstrophysicsLecture 35Terry HerterBonus lectureA2290-35 Active Galaxies 2Outline Active Galaxies Luminosities & Numbers Descriptions Seyfert  Radio Quasars Powering AGN with Black Holes What powers these things? Size limits. Standard model (accretion disk around black hole) Eddington Luminosity Limit on luminosity depends on size of black holeActive GalaxiesA2290-35 2A2290-35 Active Galaxies 3Galaxies exist which have luminosities much greater than the Milky Way (our Galaxy). In some cases more than a thousand times brighter What are they? What makes them shine so brightly“Galaxies” Luminosity (LMW*) CommentNormal < 10Seyfert 0.5 - 50 spiral w/ bright nucleusRadio 0.5 - 50 radio bright ellipticalQuasar 100 - 5,000 star-like in appearance*where LMW= Luminosity of the Milky Way ~ 2 x 1010LsunActive GalaxiesA2290-35 Active Galaxies 4Rough Local Space Densities10-9Radio-Loud Quasars10-7Radio-Quiet Quasars10-6Radio Galaxies10-4Seyfert Galaxies10-2Luminous Spirals10-1Field GalaxiesNumber/Mpc3Object TypeFrom Osterbrock, 1989, (AGN)2Active GalaxiesA2290-35 3A2290-35 Active Galaxies 5Seyfert Galaxies 1943 – Carl Seyfert, strong nuclear emission  Seyfert 1 and 2 – broad vs. narrow wings on spectral lines Spectral lines don’t resemble normal stars. Highly ionized heavy elements, e.g. iron! Lines very “wide”  tremendously hot (>108K) or rapidly rotating (~1000 km/s) Nearly all emission comes from the galactic nucleus (a small central region). ~ 104times brighter than the center of our galaxy Emitted energy varies with time! Compact source of energy Emitting region < 1 lyr across Most energy emitted in infrared and radio parts of the spectrum. Look very much the same as normal galaxies in the visual.A2290-35 Active Galaxies 6Radio Galaxies Very bright in the radio  Cosmic rock stations? Core-Halo radio galaxies Most emission from a very small core (< 1 parsec across) Extended (or Lobe) radio galaxies Emission extends hundreds of kiloparsecs!Active GalaxiesA2290-35 4A2290-35 Active Galaxies 7Core-Halo Radio GalaxiesM87jetbright coreextended halov ~ 0.1 c in jetA2290-35 Active Galaxies 8M87Optical ImageOptical JetHST ImageActive GalaxiesA2290-35 5A2290-35 Active Galaxies 9Extended Radio Galaxies Radio LobeVisible Galaxy> 200,000 pcA2290-35 Active Galaxies 10Cygnus A“Original” extragalactic radio source, Cygnus A. ~120 kpcActive GalaxiesA2290-35 6A2290-35 Active Galaxies 11Centaurus A (Peculiar Galaxy)Nearest Radio GalaxyA2290-35 Active Galaxies 12Centaurus A (Peculiar Galaxy)Radio emission (green)Active GalaxiesA2290-35 7A2290-35 Active Galaxies 13Quasars Galaxies with extremely luminous sources  Look like stars in photographs. Some evidence of faint “parent” galaxy Energy originates in a very small region Quasars are variable Can see to great distances Most distant objects seen in the universe Such a source at 50 pc (163 lyr) would appear as bright as the Sun!A2290-35 Active Galaxies 14What powers these objects? We need to produce up to 5000 times the luminosity of the M.W. But within a region ~ 1 pc in size !!!! Less than the distance between the Sun and its nearest neighbor Leading theory is a black hole with an accretion disk: Material gains energy as it falls towards the black hole. The gas heats up, and radiates energy.Active GalaxiesA2290-35 8A2290-35 Active Galaxies 15Accretion disk modeljets of highspeed particlesAccretiondiskGas fallingonto diskblack holeA2290-35 Active Galaxies 16Accretion DisksNGC 4261Black Hole Disk ModelActive GalaxiesA2290-35 9A2290-35 Active Galaxies 17Energetics Material needs to keep flowing onto the black hole to power the source.  For 1 Msun/ decade  ~ 10 LMW For 10,000 LMW 100 Msun/ year!! Large black holes (108-109Msun) are needed, otherwise the accretion disks blow themselves apartA2290-35 Active Galaxies 18What makes AGN tick? Over the last decade or more, a “standard model” of AGN has developed. The aim of this standard model is to explain and unify the plethora of observed phenomena. The following slides go into more of the details of structure about the black hole and limits to the luminosity Some of this material is a bit more advanced but is within the scope of what we have already coveredFigures that follow are from Merrifield and can be found at http://www.astro.soton.ac.uk/PH308/AGN/Seyferts.htmlActive GalaxiesA2290-35 10A2290-35 Active Galaxies 19 Central engine Surrounded by an accretion disk powers the source High energy electrons are ejected at the poles Broad line clouds are close to the monster High Keplerian velocities give broad lines A dust torus surrounds the central engine, and broad line region. “Narrow line” clouds surround are located outside torus.AGN Standard ModelA2290-35 Active Galaxies 20Spiral Host GalaxySeyfert 2Seyfert 1 The observed spectrum and continuum will depend on the viewing direction.Active GalaxiesA2290-35 11A2290-35 Active Galaxies 21Elliptical Host GalaxyRadio GalaxyBL Lac The observed spectrum and continuum will depend on the viewing direction.Name taken from prototype thought to be a variable star in Lacerta constellation. Have a smooth continuum (lack of spectral lines)A2290-35 Active Galaxies 22Mass of the Central Object An estimate of the mass of the central source for AGN can be made with two simple assumptions Isotropy Stability Both of these are not entirely correct but should give reasonable limits These arguments date back to Zel’dovich and Novikov (1964) and Salpeter (1964) Much of the discussion here follow that of Peterson (1997) See Krolick (1999) for a more detailed discussion We will use “conventional units” in the following discussionActive GalaxiesA2290-35 12A2290-35 Active Galaxies 23Radiation Pressure Consider a parcel of gas located a distance r from an central source of luminosity L. The flux from the central source (ignoring the intervening opacity) at this distance is: The momentum carried by a photon is E/c, so that the outward momentum flux (photon pressure) is:24 rLFcrLcFPrad24A2290-35 Active Galaxies 24Force due to Radiation Pressure In general, the opacity of the gas will be very complicated. If the gas is completely ionized