Vatican 2003 Lecture 30 HWR Black Holes

Vatican 2003 Lecture 30 HWR Black Holes and Galaxy Centers Two most important energy production mechanisms in astrophysics: nuclear fusion (e.g. stars)E fusion ~ mc² gravitational accretion onto “deep potential wells” –such as white dwarfs, neutron stars & black holes –requires conversion of: potential energy  thermal energy  radiation E accretion ~  mc 2 /2 with  : efficiency for black holes  Accretion onto black holes could be the most efficient energy production mechanism, IF black holes are abundant!

Vatican 2003 Lecture 30 HWR Do Black Holes Exist? A brief History Late 60‘s: Zeldovich, Lynden-Bell, Salpeter and others considered that –QSOs (“Quasi-stellar Objects”) have “sustained” luminosities of ~10 46 ergs/sec –flux variability (at short wavelengths) at t var ~ hours  r flux ~ t var · c  luminosity equal to a whole galaxy from a region the size of the solar system  accretion onto BH only sustainable and viable energy production mechanism To sustain accretion, F radiation < -F grav on electrons (“Eddington limit”):  L QSO  M BH x M sun  “Super-massive black holes” (SMBH)

Vatican 2003 Lecture 30 HWR How to detect a black hole? A. Criteria demonstrate the existence of an event horizon “relativistically deep” potential well –gravitational redshift of light –Doppler boosting, transverse Doppler effect, etc. –show relativistic (v  0.1 c) material motion exclude alternative explanations e.g. lower limit on dynamical mass + upper limit on emitted radiation  astrophysical “mass-to-light-ratio” limit from considering alternatives: –clusters of neutron stars –clusters of planets, etc. –must be stable for t ~ t universe ~ years

Vatican 2003 Lecture 30 HWR 1. Fe - K  lines (X-ray spectroscopy) for few objects (~ 6.5 keV) –emission from very hot plasma –line widths and line shapes match expectations for material orbiting v  0.3 c –in a few cases last stable orbit implies SMBH of high spin B. Methods Two separate issues: qualitative proof existence and estimate/measurement of masses (and spin) Predicted Emission Line Profiles for  Schwarzschild and Kerr Black Holes

Vatican 2003 Lecture 30 HWR Observed K  Lines X-ray observations of galaxy centers: we see gas move at relativistic speeds  close to last stable orbit

Vatican 2003 Lecture 30 HWR Relativistic Jets in AGNs Require Black Holes

Vatican 2003 Lecture 30 HWR Broad Optical/UV Emission Lines in Active Galactic Nuclei Ha several 1000km/s wide!!

Vatican 2003 Lecture 30 HWR Measuring Black Hole Masses Example 1: NGC4258 the nucleus of the nearby spiral galaxy shows several spots of H 2 O maser emission (Myashi etal 1995) Velocities and positions fit a Keplerian disk perfectly   > 5x10 12 M sun /pc 3

Vatican 2003 Lecture 30 HWR NGC4258 (cntd.)

Vatican 2003 Lecture 30 HWR Example 2: the Galactic Center Genzel, Eckardt,Schoedel et al Ghez et al 1995 – At the geometric center of the Milky Ways inner stellar mass distribution lies the radio source SgrA* Is it a black hole? Method: at only 10kpc distance, we can watch stars move G.C. seen with the VLT: Schoedel et al

Vatican 2003 Lecture 30 HWR Orbit of one star over the last 10 years Stellar Motions in the G.C. Stellar distribution in the G.C.

Vatican 2003 Lecture 30 HWR Black Holes in Nearby Nuclei Example 3: M32 (van der Marel, de Zeeuw & Rix, 1997) Stellar density   stars, then add  BH Compare predicted stellar kinematics with HST data M BH ~3x10 6 M Sun

Vatican 2003 Lecture 30 HWR Census of Nearby Black Holes Employing “broad brush” methods: Whenever a “non-luminous”, compact mass excess (“M DO ”) in galaxy centers could be studied, an SMBH is the only viable explanation.  attempt census of M DO ‘s and identify with M BH HST with its superior resolution has been pivotal in such studies e.g. Gebhardt et al 2002 Questions: Do all galaxies have black holes at their centers? Do big (i.e. massive) black holes live in big galaxies?

Vatican 2003 Lecture 30 HWR M BH and Host Galaxy Properties Magorrian et al. 1998: claimed that more luminous galaxies have more massive black hole measurements. [all their BH measurements were spurious, though] Ferrarese & Merrit, 2000; Gebhardt et al 2000: M BH ~   n M BH can be predicted from the velocity dispersion at 1kpc No good physical explanation, yet.

Vatican 2003 Lecture 30 HWR M BH vs M stars and Concentration The black hole mass seems to correlate well with many global properties of the galaxy’s bulge (not disk!!) E.g. Haering & Rix 2003: M BH vs M stars M-  relation is an easy way to measure M BH from   Mean density of BH today  BH)  5  10 5 M  / Mpc3

Vatican 2003 Lecture 30 HWR Measuring Black Holes in High-Redshift Galaxies Reverberation mapping: Measure light-travel time between –accretion disk at the very center (continuum) –Broad line region Measure velocity width of broad lines  M BH ~  2 BLR xR/G Netzer, Peterson, Maoz, Kaspi and others

Vatican 2003 Lecture 30 HWR Reverberation Mapping of QSOs QSO Spectra..and their time variation

Vatican 2003 Lecture 30 HWR Reverberation Mapping of QSOs Line – cont. time-lag Eddington limit  Most luminous QSO‘s have   0.1

Vatican 2003 Lecture 30 HWR How Early Did Massive Black Holes Exist? Pentericci et al 2001 Very Luminous QSOs exist at z>6! “Eddington Limit”: Gravitational force inward > Radiation Force Outward  M BH > 10 9 M Sun 0.6 Gyrs after the Big Bang Questions: How did massive Black Holes get to the to galaxy centers in the first place? How did they grow in mass?

Vatican 2003 Lecture 30 HWR Black Hole Growth Increase in total mass (integrated over all black holes): Accretion onto the black hole Individual mass increase: Accretion or Merging

Vatican 2003 Lecture 30 HWR QSO Luminosity Function and BH Growth QSO luminosity function varies widely as a function of z Yu & Tremaine 2002 Are present day black holes the result of luminous accretion in QSO phases?  BH, QSO  3-5  10 5 M   Mpc (0.1/  )

Vatican 2003 Lecture 30 HWR Black Hole Merging BH’s sit at the centers of every (most) (proto-)galaxy Early galaxies (and their halos) merge What happens to the black holes at their centers? Step 1: –Black holes in central cusps sink to the –center via dynamical friction, until i.e. the BH’s dominate the mass in the center Step 3: –Black holes spiral in, emitting gravitational radiation Step 2: a hang-up > 100 a grav.rad !! How to get from 1 to 3 ??

Vatican 2003 Lecture 30 HWR Black Hole Merging in a Cosmological Context Volonteri et al. 2003: Start with M BH ~200 M Sun in every sub-halo Follow merging tree  can get 10 8 M Sun by now  But : it is hard to get 10 9 by z~6 Question: what was the initial black hole mass?

Vatican 2003 Lecture 30 HWR Initial Black Holes Possible Key: Very first generation of stars (Pop III) No metals  no cooling  gas clouds stay hotter  Jeans mass is higher (where fragmentation sets in)  first stars very massive Possible masses 200 M Sun 10 6 M Sun (?) Bromm etal 1999,2003, Abell et al 2000 Formation of 10 5 MSun star at z~30 (Bromm and Loeb 2003)

Vatican 2003 Lecture 30 HWR Overall Census All galaxies with bulges seem to have black holes The black hole mass correlates tightly with the overall mass and dynamics of the host bulge Averaging over the galaxy population in the present day universe, the mean black hole density is ~5x10 5 M Sun /Mpc 3 (Yu & Tremaine 2003)  BH growth and bulge formation are connected E.g. both happen during mergers with gas inflow Black holes grow through (luminous) accretion  were all galaxies QSOs sometime in the past? How important is the merging of BH’s during the merging of their galaxies? Not clear yet!