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Astrophysical Black Holes: Astrophysical Black Holes: Key QuestionsKey Questions

Avi Loeb

Harvard University

Fourth Sackler conference, May 15-18, 2006

Key questionsKey questions• Is general relativity the correct description of strong gravity?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? What is the spin and mass distribution of astrophysical black holes? Why?Why?

• What is the history of black hole formation and evolution? What is the history of black hole formation and evolution? How did the first black holes form? How did the first black holes form? Was growth dominated by accretion of gas, consumption of stars or mergers? Do Was growth dominated by accretion of gas, consumption of stars or mergers? Do binaries coalesce? What is the impact of gravitational-wave recoil?binaries coalesce? What is the impact of gravitational-wave recoil?

• How do black holes accrete gas? How do black holes accrete gas? What are the geometry and radiative efficiency of the accretion flow as a function of 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?the accretion rate? Which fraction of the infalling mass is expelled in outflows?

• In what form do black holes release accretion energy? In what form do black holes release accretion energy? What is What is the relative fraction of radiation, magnetically-dominated outflows, relativistic the relative fraction of radiation, magnetically-dominated outflows, relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic jets produced? Are they made of e+e- or baryons?jets produced? Are they made of e+e- or baryons?

• How do nuclear black holes influence the evolution of their host How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-scale intergalactic medium?galaxies, X-ray clusters, or the larger-scale intergalactic medium? What is the origin of the correlations between What is the origin of the correlations between black hole mass and spheroid properties?black hole mass and spheroid properties? What sets the maximum mass of galaxies?What sets the maximum mass of galaxies?

The Black Hole in the Galactic Center: SgrA*

VLT with Adaptive Optics

•“3-color”: 1.5 - 3 um

• 8.2 m VLT telescope

• CONICA (IR camera)

• NAOS (adaptive optics)

• 60 mas resolution

Simultaneous fit of orbits implies:

1. BH mass:

2. BH proper motion: < 0.8+-0.7 mas/yr

(4æ0:3) â (d=8kpc)3 â 106M ì

Ghez et al. 2003

SO-16 closest approach at 90 AU

Genzel et al 2003

Water Masers: NGC 4258

Moran, Greenhill, & Herrnstein (2000)

Keplerian Velocity Profile

Miyoshi et al. 1995

Broderick & Loeb 2005

Is general relativity a valid description of strong gravity?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

What is the spin distribution of What is the spin distribution of astrophysical black holes?astrophysical black holes?

Volonteri, Madau, Quataert, & Rees (2005)

Contribution from Gas accretion dominates

over mergers

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

The First Dark Matter Objects in the Universe

Smallest dark matter clumps: ~0.1 Jupiter mass

Loeb & Zaldarriaga, astro-ph/0504112

Diemand, Moore & Stadel astro-ph/0501589

Emergence of the First Star Clusters

molecular hydrogen

Yoshida et al. 2003

Cooling Rate of Primordial Gas

n=0.045 cm^-3

Atomic cooling

H_2 cooling

Virial Temperature of Halos

1-sigma 2-sigma

3-sigma

Atomic cooling

H_2 cooling

Massive Accretion by Pop-III Proto-StarsMassive Accretion by Pop-III Proto-Stars

23.5pc 0.5pc

Bromm & Loeb, New Astronomy, 2004; astro-ph/0312456

Resolving accretion flow down to ~0.03 pc

Formation of Massive Black Holes in the First Galaxies

Add Bromm

Low-spin systems: Eisenstein & Loeb 1995

Numerical simulations: Bromm & Loeb 2002

R < 1pc

M 1 ø 2:2â 106M ì

M 2 ø 3:1â 106M ì

õ = 0:05

H2 suppressed

Supermassive StarsSupermassive Stars

Teff ø 105K

L = L E / M

For a spherical (non-rotating) star:general-relativistic instability at

(Rc2GM)crit = 0:6295( M

M ì )1=2

Angular momentum mass shedding along equator

Collapse to a black hole is inevitable for M > 300M ì

High spin disks: Loeb & Rasio 93; Low-spin disks: Eisenstein & Loeb 95

S. Shapiro, et al. 2003

Growth of Supermassive Black HolesGrowth of Supermassive Black Holes

tE = M=Mç = 4â 107(L=L E)(ï=10%)years

L = ïMçc2

M / expf t=tEg

Why Are Quasars Short Lived?Why Are Quasars Short Lived?

Principle of Self Regulation: supermassive black holes grow until they release sufficient energy to unbind the gas that feeds them from their host galaxy

Because they are suicidal!

Implies a correlation between black hole mass and the depth of the gravitational potential well of its host galaxy

(M bh=M galaxy) < 10à 3(NQuasars=NGalaxies) < 10à 2 ;

Quasar Luminosity Function

Wyithe & Loeb astro-ph/0304156

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

M ï / v5c

Hydrodynamic Simulations of Quasar FeedbackHydrodynamic Simulations of Quasar Feedback

Springel, Hernquist, Di Matteo et al. 2005

Hydrodynamic Simulations of Quasar FeedbackHydrodynamic Simulations of Quasar Feedback

Mç = minfBondi à rate;Eddington à rategenergy à feedingà rate= 5%â 10%â Mçc2

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

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

How do black holes accrete gas?How do black holes accrete gas?

Stone et al. 2005

What is the accretion rate into SgrA*horizon?

MçB ø 10à 5M ì yrà 1

Bolometric luminosity: ø 1036erg=s

Mç ø 2â 10à 10M ì yrà 1(ï=0:1)à 1

Bondi rate:

Feeding SgrA* with Stellar Winds

Loeb, astro-ph/0311512

J < J max = ñ c4GM ï

ð ñEmission region:Emission region:

In what form do black holes In what form do black holes release accretion energy?release accretion energy?

• Radiation

• Non-relativistic wind

• Relativistic particles and magnetized jets

• Neutrinos

• Gravitational radiation

Injection of Positrons from AGN Jets

Furlanetto& Loeb 2002

e+e- jet

Spectrum of Positron Annihilation Line3-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 100 Mpc

More details: ApJ, 572, 796 (2002)

Black Hole Binaries due to Galaxy Mergers

X-ray Image of a binary black hole system in NGC 6240

Komossa et al. 2002

z=0.025

Dynamics of black hole binaries

Chatterjee, Hernquist, & Loeb 2002

Figure1.ps

Typical binaries coalesce in less than 10 Gyr due to wandering

Numerical experiment:

400,000 stars

M=M ? = 0:25%

kick velocity from galaxies

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

Gravitational Radiation from Coalescence of Massive Black Hole Binaries

Wyithe & Loeb 2002

PULSARS

REDSHIFT FREQUENCY (Hz)

How do nuclear black holes influence the evolution How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-of their host galaxies, X-ray clusters, or the larger-

scale intergalactic medium?scale intergalactic medium?

Fabian et al. 2003Kraft et al. 2005

• 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?

McNamara et al. 2005 Forman et al. 2003

Correlation between black hole mass and velocity dispersion of host stellar system

Tremaine et al. 2002

ì = 4:02æ0:32;ë = 8:13æ0:06

ë = 8:22æ0:07

ì = 4:58æ0:52

Ferrarese 2002

log(M=M ì ) = ë + ì log(û?=200km=s)

Self-regulation of Supermassive Black Hole Growth

quasar

! 108M ì

M bh = 1:5 200km=sû

ð ñ5

Ltdyn ø 23M gasû2

dynamical time of galactic disk maxf Lg = L E / M bh

halo velocity dispersion

After translating û ! û? this relation matches the observed correlation in nearby galaxies (Tremaine et al. 2002; Ferarrese & Merritt 2002)

M à ûã

Silk &Rees 1998; Wyithe & Loeb 2003

M bh / f ?

â (1+ z)3=2

Clustering Statistics of QuasarsClustering Statistics of Quasars

Wyithe & Loeb 2004; Wyithe & Loeb 2004; astro-ph/0403714astro-ph/0403714

Lines:Lines: correlation function of model with

L = L E

M bh / v5c

Data points:Data points:

2dF Quasar Survey (Boyle et al. 2000)

Data on Quasar Clustering/LF Implies:Data on Quasar Clustering/LF Implies:

M bh / v5c

M bh / M 5=3halo

• 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 / (1+ z)à 3=2

tE = 4â 107(ï=0:1)years

Wyithe & Loeb 2004; astro-ph/0403714Wyithe & Loeb 2004; astro-ph/0403714

Effects of Quasars on the Intergalactic Medium: Ionization and Magnetization

The Earliest Quasar Detected:The Earliest Quasar Detected: zz=6.4=6.4

Fan et al. 2002

Cosmic Hydrogen was significantly Neutral at z~6.3Cosmic Hydrogen was significantly Neutral at z~6.3

Wyithe & Loeb, Nature, 2004; astro-ph/0401188

Size of HII region depends on neutral fraction of IGM prior to quasar activity and quasar age

Ionization(Stromgren) sphere of quasar

line of sight

Cosmic Background Radiation

Gamma-ray background

Quasars as Perturbers:Impact of Quasar Outflows on the IGM

Furlanetto & Loeb 2001

Intergalactic Medium (IGM)

Is the IGM fully magnetized just like the ISM?

jetBAL outflow

quasar

small-scale structure; magnetization; ionization

Magnetized bubble

Volume Filling Factor of Quasar Bubbles

Magnetic energy density normalized by thermal at 10^4 K

Volume filling factor of IGM

Probability Distribution of Bubble Radius

*Magnetic pressure larger minimum b-parameter of Lya forest

Probability Distribution of Bubble Magnetic Field

*Could account for intra-cluster and galactic fields through adiabatic compression. Explains synchrotron halos of clusters.

B / ú2=3

Key questionsKey questions• Is general relativity the correct description of strong gravity?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? What is the spin and mass distribution of astrophysical black holes? Why?Why?

• What is the history of black hole formation and evolution? What is the history of black hole formation and evolution? How did the first black holes form? How did the first black holes form? Was growth dominated by accretion of gas, consumption of stars or mergers? Do Was growth dominated by accretion of gas, consumption of stars or mergers? Do binaries coalesce? What is the impact of gravitational-wave recoil?binaries coalesce? What is the impact of gravitational-wave recoil?

• How do black holes accrete gas? How do black holes accrete gas? What are the geometry and radiative efficiency of the accretion flow as a function of 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?the accretion rate? Which fraction of the infalling mass is expelled in outflows?

• In what form do black holes release accretion energy? In what form do black holes release accretion energy? What is What is the relative fraction of radiation, magnetically-dominated outflows, relativistic the relative fraction of radiation, magnetically-dominated outflows, relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic particles, non-relativistic winds, neutrinos, gravitational waves?How are relativistic jets produced? Are they made of e+e- or baryons?jets produced? Are they made of e+e- or baryons?

• How do nuclear black holes influence the evolution of their host How do nuclear black holes influence the evolution of their host galaxies, X-ray clusters, or the larger-scale intergalactic medium?galaxies, X-ray clusters, or the larger-scale intergalactic medium? What is the origin of the correlations between What is the origin of the correlations between black hole mass and spheroid properties?black hole mass and spheroid properties? What sets the maximum mass of galaxies?What sets the maximum mass of galaxies?

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

Dynamics of Black Holes and Dynamics of Black Holes and Stars in Galactic NucleiStars in Galactic Nuclei

Could the close-in massive Starsoriginate in a warm molecular (maser) disk?

• 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.

Milosavljevic & Loeb astro-ph/0401221

T > 400K;n ø 107à 1010cmà 3

M disk ø 104M ì â n9r7=23 T1=2

4 Mà 1=27

Q ü 1

What is the accretion rate into SgrA*horizon?

MçB ø 10à 5M ì yrà 1

Bolometric luminosity: ø 1036erg=s

Mç ø 2â 10à 10M ì yrà 1(ï=0:1)à 1

Bondi rate:

Feeding SgrA* with Stellar Winds

Loeb, astro-ph/0311512

J < J max = ñ c4GM ï

ð ñEmission region:Emission region:

Brownian Motion of a Massive Black Hole in a Stellar System

Chatterjee, Hernquist, & Loeb 2001 (ApJ, PRL)

For a non-Maxwellian distribution function of stars the black hole is not in strict equipartition

Probing the Spacetime Around SgrA* with Pulsars

• 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/0309744)

~10-100 massive stars with P<100 yr and lifetime of ~ 107 years~1000 NS in steady state 1-10 detectable pulsars at 10-20 GHz

Laser Interferometer Space Antenna

Binding Energy of Halos

1-sigma 2-sigma

3-sigma

Supernova

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