2. Discuss topics in sequence with the question at the top of each slide.

3. Astrophysical Black Holes: Key Questions
Avi Loeb
Harvard University
Fourth Sackler conference, May 15-18, 2006

4. Key questions
Is general relativity the correct description of strong gravity? Do black holes exist?Are they described by the Kerr metric (with the predicted properties of the event horizon, innermost stable circular orbit, photon orbit, etc.)?
What is the spin and mass distribution of astrophysical black holes? Why?
What is the history of black hole formation and evolution? How did the first black holes form? Was growth dominated by accretion of gas, consumption of stars or mergers? Do binaries coalesce? What is the impact of gravitational-wave recoil?
How do black holes accrete gas? What are the geometry and radiative efficiency of the accretion flow as a function of the accretion rate? Which fraction of the infalling mass is expelled in outflows?
In what form do black holes release accretion energy? What is the relative fraction of radiation, magnetically-dominated outflows, relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic jets produced? Are they made of e+e- or baryons?
How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-scale intergalactic medium? What is the origin of the correlations between black hole mass and spheroid properties? What sets the maximum mass of galaxies?

5. The Black Hole in the Galactic Center: SgrA* VLT with Adaptive Optics
“3-color”: um
8.2 m VLT telescope
CONICA (IR camera)
NAOS (adaptive optics)
60 mas resolution

6. Ghez et al. 2003 Genzel et al 2003 SO-16 closest approach at 90 AU
Simultaneous fit of orbits implies:
1. BH mass:
2. BH proper motion: < mas/yr

7. Water Masers: NGC 4258
Moran, Greenhill, & Herrnstein (2000)

8. Keplerian Velocity Profile
Miyoshi et al. 1995

9. Is general relativity a valid description of strong gravity?
*Infrared variability of flux (Genzel et al.) and polarization (Eckart et al.) of SgrA*: hot spots.
*Innermost Stable Circular Orbit: radius of 30 (10) micro-arcsecond and orbital time of 30 (8) minutes for a non-rotating (maximally-rotating) black hole at the Galactic center
*A hot spot would result in infrared centroid motion (PRIMA-VLT) and could be imaged by a Very Large Baseline Array of (existing) sub-millimeter observatories. Targets:SgrA* and M87
Broderick & Loeb 2005

10. What is the spin distribution of astrophysical black holes?
Contribution from Gas accretion dominates over mergers
Volonteri, Madau, Quataert, & Rees (2005)

11. What is the history of black hole formation and evolution?

12. The First Dark Matter Objects in the Universe
Smallest dark matter clumps: ~0.1 Jupiter mass
Diemand, Moore & Stadel astro-ph/
Loeb & Zaldarriaga, astro-ph/

13. Emergence of the First Star Clusters
molecular hydrogen
Yoshida et al. 2003

14. Cooling Rate of Primordial Gas
n=0.045 cm^-3
Atomic cooling
H_2 cooling

15. Virial Temperature of Halos
Atomic cooling
H_2 cooling
3-sigma
1-sigma
2-sigma

16. Massive Accretion by Pop-III Proto-Stars
23.5pc
0.5pc
Resolving accretion flow down to ~0.03 pc
Bromm & Loeb, New Astronomy, 2004; astro-ph/

17. Formation of Massive Black Holes in the First Galaxies
Add Bromm
Low-spin systems: Eisenstein & Loeb 1995
Numerical simulations: Bromm & Loeb 2002

18. Supermassive Stars For a spherical (non-rotating) star:
general-relativistic instability at
Angular momentum mass shedding along equator
Collapse to a black hole is inevitable for
S. Shapiro, et al. 2003
High spin disks: Loeb & Rasio 93; Low-spin disks: Eisenstein & Loeb 95

19. Growth of Supermassive Black Holes

20. Why Are Quasars Short Lived?;
Why Are Quasars Short Lived?
Because they are suicidal!
Principle of Self Regulation: supermassive black holes grow until they release sufficient energy to unbind the gas that feeds them from their host galaxy
Implies a correlation between black hole mass and the depth of the gravitational potential well of its host galaxy

21. Quasar Luminosity Function
Simple physical model:
*Each galaxy merger leads to a bright quasar phase during which the black hole grows to a mass and shines at the Eddington limit. The duration of this bright phase is dictated by the dynamical time of the host galactic disk (7% of the total energy release can unbind the disk on its dynamical time).
*Merger rate: based on the extended Press-Schechter model in a LCDM cosmology.
duty cycle ~10 Myr
Wyithe & Loeb astro-ph/

22. Hydrodynamic Simulations of Quasar Feedback
Springel, Hernquist, Di Matteo et al. 2005

23. Hydrodynamic Simulations of Quasar Feedback
(Springel, Di Matteo, & Hernquist 2004)

24. (Springel, Di Matteo, & Hernquist 2004)

25. How do black holes accrete gas?
Stone et al. 2005

26. What is the accretion rate into SgrA*horizon?
Bolometric luminosity:
Bondi rate:

27. Feeding SgrA* with Stellar Winds
Emission region:
Loeb, astro-ph/

28. In what form do black holes release accretion energy?
Radiation
Non-relativistic wind
Relativistic particles and magnetized jets
Neutrinos
Gravitational radiation

29. Injection of Positrons from AGN Jets
e+e- jet
AGN
X-ray cluster
Furlanetto& Loeb 2002

30. Spectrum of Positron Annihilation Line
3-photon decay of Positronium does not smear line due to keV temperature of cluster electrons (direct annihilation more probable)
Line signal detectable with INTEGRAL (launched Oct. 2002) and EXIST (space station) for rich X-ray clusters out to Mpc
More details: ApJ, 572, 796 (2002)

31. Black Hole Binaries due to Galaxy Mergers

32. X-ray Image of a binary black hole system in NGC 6240
10kpc
z=0.025
Komossa et al. 2002

33. Dynamics of black hole binaries
wandering R
Figure1.ps
Numerical experiment:
400,000 stars
Typical binaries coalesce in less than 10 Gyr due to wandering
Chatterjee, Hernquist, & Loeb 2002

34. kick velocity from galaxies

35. Gravitational Wave Amplitude from a Black Hole Binary at z=1

36. Gravitational Radiation from Coalescence of Massive Black Hole Binaries
PULSARS
LISA
REDSHIFT
FREQUENCY (Hz)
Wyithe & Loeb 2002

37. How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-scale intergalactic medium?
Fabian et al. 2003
Kraft et al. 2005
McNamara et al. 2005
Forman et al. 2003
What is the dominant mechanism that mediates the energy transfer? acoustic waves, relaticistic particles and magnetic fields
Is the growth of the stellar spheroid affected by this feedback?

38. Correlation between black hole mass and velocity dispersion of host stellar system
Tremaine et al. 2002
Ferrarese 2002

39. Self-regulation of Supermassive Black Hole Growth
quasar
dynamical time of galactic disk
halo velocity dispersion
galactic disk
After translating
this relation matches the observed correlation in nearby galaxies (Tremaine et al. 2002; Ferarrese & Merritt 2002)
Silk &Rees 1998; Wyithe & Loeb 2003

40. Clustering Statistics of Quasars
Lines: correlation function of model with
(SIS)
Data points:
2dF Quasar Survey (Boyle et al. 2000)
Wyithe & Loeb 2004; astro-ph/

41. Data on Quasar Clustering/LF Implies:
Local relation between galactic halo/black-hole + redshift evolution of quasar correlation length are consistent with
and not
If mergers trigger quasar activity, then quasar lifetime scales with dynamical time of host galaxy
rather than the redshift-independent Salpeter-Eddington time for its growth
Wyithe & Loeb 2004; astro-ph/

42. Effects of Quasars on the Intergalactic Medium: Ionization and Magnetization

43. The Earliest Quasar Detected: z=6.4
Fan et al. 2002

44. Cosmic Hydrogen was significantly Neutral at z~6.3
Ionization(Stromgren) sphere of quasar
Size of HII region depends on neutral fraction of IGM prior to quasar activity and quasar age
line of sight
R(t)
Wyithe & Loeb, Nature, 2004; astro-ph/

45. Cosmic Background Radiation
Gamma-ray background

46. Quasars as Perturbers: Impact of Quasar Outflows on the IGM
small-scale structure; magnetization; ionization
BAL outflow
jet
Magnetized bubble
Intergalactic Medium (IGM)
quasar
Is the IGM fully magnetized just like the ISM?
Furlanetto & Loeb 2001

47. Volume Filling Factor of Quasar Bubbles
Volume filling factor of IGM
Magnetic energy density normalized by thermal at 10^4 K

48. Probability Distribution of Bubble Radius
*Magnetic pressure larger minimum b-parameter of Lya forest

49. Probability Distribution of Bubble Magnetic Field
*Could account for intra-cluster and galactic fields through adiabatic compression. Explains synchrotron halos of clusters.

50. Key questions
Is general relativity the correct description of strong gravity? Do black holes exist?Are they described by the Kerr metric (with the predicted properties of the event horizon, innermost stable circular orbit, photon orbit, etc.)?
What is the spin and mass distribution of astrophysical black holes? Why?
What is the history of black hole formation and evolution? How did the first black holes form? Was growth dominated by accretion of gas, consumption of stars or mergers? Do binaries coalesce? What is the impact of gravitational-wave recoil?
How do black holes accrete gas? What are the geometry and radiative efficiency of the accretion flow as a function of the accretion rate? Which fraction of the infalling mass is expelled in outflows?
In what form do black holes release accretion energy? What is the relative fraction of radiation, magnetically-dominated outflows, relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic jets produced? Are they made of e+e- or baryons?
How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-scale intergalactic medium? What is the origin of the correlations between black hole mass and spheroid properties? What sets the maximum mass of galaxies?

51. The organizing committee will regard this conference as a success if it will result in a new answer to any of these questions…

53. Dynamics of Black Holes and Stars in Galactic Nuclei

54. Could the close-in massive Stars originate in a warm molecular (maser) disk?
Milosavljevic & Loeb astro-ph/
In maser disks:
comparable to the circumnuclear disk in the Galactic center.
clumps IRS13 complex at 0.12pc
Eccentricity in orbits from stellar interactions.
Heating by X-rays from AGN or by stars.

55. What is the accretion rate into SgrA*horizon?
Bolometric luminosity:
Bondi rate:

56. Feeding SgrA* with Stellar Winds
Emission region:
Loeb, astro-ph/

57. Brownian Motion of a Massive Black Hole in a Stellar System
For a non-Maxwellian distribution function of stars the black hole is not in strict equipartition
Chatterjee, Hernquist, & Loeb 2001 (ApJ, PRL)

59. Probing the Spacetime Around SgrA* with Pulsars
~ massive stars with P<100 yr and lifetime of ~
~1000 NS in steady state
1-10 detectable pulsars at GHz
BH spin vector from frame-dragging + imaging of pulsar orbit
Inner stellar cluster from gravitational scattering events
Test accretion flow models by measuring plasma density
Pfahl & Loeb 2003 (astro-ph/ )

60. Laser Interferometer Space Antenna

62. Binding Energy of Halos
Supernova
3-sigma
1-sigma
2-sigma