Quasars ASTR 2120 Sarazin Quintuple Gravitational Lens Quasar
Quasars Quasar = Quasi-stellar (radio) source Optical: faint, blue, star-like objects Radio: point radio sources, faint blue star-like optical counterparts, 10% radio-loud
Quasars - Optical Spectra Quasars are distant, high-redshift objects 0.1 z 8
Quasars Quasars are distant, high-redshift objects 0.1 z 8 <z> 2
Quasars
Quasars - What Are They? Optical Properties: Very similar to Seyferts and other AGN except more luminous Radio Properties (Radio-Loud Quasars): Very similar to Radio Galaxies, have radio lobes and jets, but core is more luminous
Quasars - What Are They? Optical Properties: Very similar to Seyferts and other AGN except more luminous Radio Properties (Radio-Loud Quasars): Very similar to Radio Galaxies, have radio lobes, but core is more luminous Normal Galaxies Seyferts, Radio Galaxies Quasars Location: Quasars = very luminous AGNs = in centers of galaxies?
Quasars = Very Luminous AGNs Quasars = very luminous AGNs = in centers of galaxies? Why weren t host galaxies seen in early observations? 1. Most at high redshift, far away, host galaxies only few arcsec across 2. Seeing in ground-based observations blurs images to few arcsec 3. AGN is ~100 x luminosity of galaxy, galaxy is buried Observe with HST!!
Quasars Host Galaxies - HST
Quasars Host Galaxies - HST
Quasars Host Galaxies - HST
Quasars = Very Luminous AGNs Quasars = very luminous AGNs = in centers of galaxies
Theory of Quasars & AGNs What is the central engine? Size 10 2 AU ~ Solar System L 10 2 galaxies!! Mass? If held together by gravity, L < L edd = 1.5 x 10 38 (M/M ) erg/s Eddington luminosity L ~ 10 47 erg/s (quasar) M 10 9 M!! (quasar)
Theory (Cont.) Motions of Broad Line Clouds Broad lines due to Doppler shifts, v ~ 10 4 km/s Ionization of clouds d ~ 0.1 pc from central engine Clouds bound to central engine Virial theorem, PE = -2 KE M ~ v 2 d / G ~ 10 9 M!! (argument general) d v
Weaker AGNs Theory (Cont.) M central ~ 10 6 to 10 9 M
Nature of Central Object Need ~10 9 M packed into ~10 AU 1) One ~10 9 M star? BH in ~10 6 years 2) 10 9 stars (or neutron stars or BHs) collide, turn into one BH very quickly 3) 10 9 M black hole!! AGNs = super-massive black holes (SMBHs) in centers of galaxies (10 6 to 10 9 M )
SMBHs in Galaxies Most large galaxies have some activity Quasars most large galaxies in the past had SMBHs, would not go away Predict: Most large galaxies today have SMBH? Detect from motion of gas, stars near center of galaxy
SMBHs in Galaxies
SMBHs in Galaxies
SMBHs in Galaxies
SMBHs in Galaxies All large galaxies have a SMBH at the center M SMBH 0.0015 M(stars in bulge) How did this occur? Suggests that SMBH and galaxies (at least bulge parts) grew together in lockstep? Why? Feedback from SMBH affects star formation? Star formation affects supply of gas to SMBH?
Size of SMBH Theory (Cont.) R = R S = 2GM/c 2 = 20 AU (M BH /10 9 M ) ~ emission region from AGN
Energy Source Massive BH and nearby gas (emission lines) = accretion? Broad lines: M gas ~ 10 2 M t infall ~ r/v ~ (0.1 pc)/(10 4 km/s) ~ 10 1 years Ṁ ~ 10 M / yr accretion rate
Accretion by BH - Review Last semester showed that: L = (1/4) (R S /R) Ṁ c 2 ~ (0.1-0.4) Ṁ c 2 for a BH L ~ 10 47 erg/s (Ṁ /10 M / yr ) ~ L quasar
Accretion Disks Last semester and with galaxy formation, saw that infall of gas generally leads to rotating disk = accretion disk BH event horizon R inner = last stable circular orbit
Accretion Disks or Torii
Accretion Disks or Torii
Accretion Disks Temperature of inner accretion disk T disk [ L / ( 2πR 2 inner σ)] 1/4 ~ 10 5-6 K for AGN UV emission = blue bump in spectrum BH event horizon R inner = last stable circular orbit
Accretion Disks Thermal emission from accretion disk radio IR visible UV X-ray
Accretion Disks Counter-intuitive aspect: Stellar BHs, M ~ 10 M SMBHs, M ~ 10 9 M SMBH accretion disks cooler Roughly, T disk M -1/4 BH Why do AGN have X-rays? T disk ~ 10 7-8 K X-rays T disk ~ 10 5-6 K UV
Magnetic Accretion Disks Gas in disks ionized, magnetic fields frozen in Magnetic fields carried in, strengthened 1. Magnetic fields provide means to carry angular momentum out, allow gas to accrete (Balbus-Hawley instability) 2. Accelerate relativistic particles (like pulsars) 3. Reconnection above disk (like solar flares) Make X-rays and gamma-rays
Magnetic Accretion Disks
Magnetic Accretion Disks 4. Make jets
Magnetically Driven Jets
Magnetically Driven Jets
Accretion Disks Can we see gas accreted by black holes? black hole event horizon
Accretion Disks Can we see gas accreted by black holes? Spectrally: Highly blueshifted and redshifted (Dopper and gravity) from accretion disk gas.
X-ray Line from Black Hole Grav. redshift Dopp redshift Dopp blueshift
Accretion Disks Can we see gas accreted by black holes? Spectrally: Highly blueshifted and redshifted (Dopper and gravity) from accretion disk gas.
Spin of Black Hole
Reverberation Mapping Bigger lags at larger radii, smaller velocities Map v(orbit) vs. radius
Athena X-ray Telescope (2028)
Measure Orbits of Blobs in Disk
Accretion Disks Can we see gas accreted by black holes? Spectrally: Highly blueshifted and redshifted (Dopper and gravity) from accretion disk gas. Imaging: Can we actually watch gas fall into black hole? Problem: Black holes are small, most far away
Event Horizon Telescope Sgr A* = biggest BH in angular size as seen from Earth Stellar mass BHs closer but 10 5 x smaller Supermassive black holes in large galaxies are up to 1000 x larger, but are much further away R Sch = 10 micro-arcseconds! Radio VLBI observations at 1.3 and 0.8 mm wavelength
Event Horizon Telescope
Event Horizon Telescope Alternative GR Alternative Black Hole Shadow on Accretion Disk
Event Horizon Telescope Accretion Disk Physics
Event Horizon Telescope Launching of Jets
Accretion Disks Can we see gas accreted by black holes? Spectrally: (and with time) Polarization: Imaging: Can we actually watch gas fall into black hole? Largest BHs in apparent size are nearby AGN Most accreted energy comes out in X-rays But, requires micro-arc-second imaging in X-rays
MAXIM: Micro-Arcsecond X-ray Interferometer Mission
X-ray Images of Black Holes with Accretion Disks
X-ray Images of Black Holes with Accretion Disks
X-ray Images of Black Holes with Accretion Disks
Unified AGN Model Type 1 Seyfert 1, Broad-Line Radio Galaxies, Quasars 1 Both Broad and Narrow Lines, Bright Type 2 Seyfert 2, Narrow-Line Radio Galaxies, Quasars 2 Only Narrow Lines, Fainter Blazars Almost no lines, very bright
Unified AGN Model Outer Accretion Disk = Accretion Torus
Unified AGN Model Accretion Torus Jet Perpendicular to Torus Narrow Line Clouds beyond Torus Broad Line Clouds inside of Torus
Unified AGN Model What we see depends on viewing angle through torus Seyfert 2, Quasar 2, Narrow Line Radio Galaxy Narrow lines, X-rays, faint over torus Seyfert 1, Quasar 1, Broad Line Radio Galaxy Broad and Narrow lines, brighter along jet Very bright, variable, lines buried in continuum
Why are quasars mainly at high redshift? As galaxies form in past, lots of gas around, new stars may be on orbits near BH high accretion rate With time, BH (and star formation) eat up most of fuel low accretion rate In present day Universe, evidence that mergers cause more activity new fuel for accretion
Gravitationally Lensed Quasars Einstein s Cross
Gravitationally Lensed Quasars Use time delay between images to measure distance to lens?
Quasar Absorption Lines Sample Intergalactic Medium Lyman alpha forest implies most of baryons in intergalactic gas (at z~2) Lyα emission line Lyα forest