Upload
jody-gibbs
View
215
Download
0
Embed Size (px)
Citation preview
Forming and Feeding Super-massive Black Holes
in the Young Universe
Wolfgang J. Duschl
Institut für Theoretische Astrophysik
Universität Heidelberg
Kyoto – 30 October 2003
Plan of talk
• Evidence for massive black holes in the (very) young Universe – Quasars
• Physics of accretion disks: Self-gravity and viscosity
• The parallel evolution of super-massive black holes and of nuclear (quasar/AGN) activity
Kyoto – 30 October 2003
The need for SMBHs in the early Universe
High redshift objects, i.e., young Universe objects:
High luminosity objects (almost entirely from their centre):
Large accretion rate objects:
Large central mass objects:
45 48 -1 12 1510 erg s 10 LQL » »L Le
min max 2apot a Black
min hole
1 1 12
1
10 M yr
r r GMML M MGM Mc
r r
LM
c
h
h- + -
æö÷ç= DF = D » =÷ç ÷çè ø
® = =
=
Le
&& & &
&
7.5 10.5a4 10
M 3.92 10 LM L
>×
L
e e
A
L: Luminosity
Ma: accreting mass
M: mass flow rate
pot: potential energy
r (rmin): (inner) radius
accretion efficiency
.
Fan et al. (2003; SDSS):QSO @ z = 6.4
Then the Universewas less than a billion years old.
Kyoto – 30 October 2003
The need for SMBHs in the early Universe
• How can one transport such large masses (up to at least 10 M yr-1) to a central black hole?
• How can such large central masses exist at all so early in the Universe? How can they be formed so quickly?
• Where have all the quasars gone? (... and why are there no new ones?)
Kyoto – 30 October 2003
The need for SMBHs in the early Universe
A scenario for the formation of super-massive black holes in quasars:
• First, tidal forces due to galaxy-galaxy interactions drive large amounts of ISM very quickly to small radii of a few 102 pc (observations: Sanders et al. 2001 …; models: e.g., Barnes & Hernquist 1996, 1999; Barnes 2002 …), until – because of the angular momentum – it gets stuck at some 102 pc.
• Subsequently, accretion – hopefully – allows to bridge the last few 102 pc, and to do so quickly (within less than 109 years).
• The two original (proto-)galaxies may or may not harbour a ((super-)massive) black hole already.
In a broader context: Post-merger evolution of the ISM in the very center of the newly formed object.
Kyoto – 30 October 2003
Plan of talk
• Evidence for massive black holes in the (very) young Universe – Quasars
• Physics of accretion disks: Self-gravity and viscosity
• The parallel evolution of super-massive black holes and of nuclear (quasar/AGN) activity
Kyoto – 30 October 2003
Accretion disk mass flow rategr, gs, gz gravitational acceleration
in r, s und z directionvs, v velocity in s und direction angular velocity in directionM* mass of accretorsa outer disk radiussi inner disk radius
density surface densityh thickness of diskT temperaturecS sound velocity viscosity time scales
Reynolds number2dz hr r+¥
- ¥
S = »ò
{s, , z; t} cylindrical coordinate system
r2 = s2 + z2
v
vs
M*, si
sa
s
z
M&
Â
Kyoto – 30 October 2003
Evolution of vicous disks
Conservation of mass and angular momentum may be combined into a single equation describing the evolution of such disks:
( )( )
3 3
Kepler
2
1 3s s
s s t s st s s s s ss
s
w wn
nw
é ùæ ö¶ ¶ ¶÷çê úS - S÷ç ÷ç é ù¶S ¶ ¶ ¶è øê ú¶ ¶ ¶= - = Sê úê ú¶ ê ú¶ ¶ ¶ ¶ê ú ë ûê ú¶ê úë û
Relevant time scales: - dynamical - viscousdyn
1t
w=
2
visc
st
n=
Kyoto – 30 October 2003
Self-gravity
Three classes of accretion disks:• Non self-gravitating (NSG)*:
– gravitational forces in the vertical and in the radial direction are dominated by the central body:
• Keplerian self-gravitating (KSG): – Self-gravity is irrelevant in the radial direction, but dominates in
the vertical direction:
• Fully self-gravitating (FSG):– Self-gravity dominates in both directions:
disk *
hM M
s=
* disk *
hM M M
s³?
* diskM M£
*: In NSG disks Shakura & Sunyaev´s a parameterization has proven to be very successful: = h cs
Kyoto – 30 October 2003
Self-gravity
Fully or Keplerian self-gravitating -disks:
i.e., the radial temperature distribution becomes independent of central mass, location within the disk, etc.
This is unphysical.
Reason: In a self-gravitating -disk the local and the global disk structure decouple.
3S
20
3dT
c GMdr
pa
= Þ =&
Kyoto – 30 October 2003
Generalized viscosity ansatz
Reynolds number based turbulence:
(Duschl, Strittmatter, Biermann 2000)
Critical issues:• Scaling parameter:
– Critical Reynolds number:– Observed velocities:
• Relation to -viscosity: Limiting case for massless disks• Linear stability: non-linear instability (e.g., Grossmann
2000; Longaretti et al. 2002); experiments (e.g., Wendt 1933; Taylor 1936)
2 3 2 3crit 10 10b - -Â = Â = Þ =L L
1with
svsvj
jn b bn
 = Þ = =Â
2turb turb( / )v v v vj jb b= Þ =
Kyoto – 30 October 2003
Plan of talk
• Evidence for massive black holes in the (very) young Universe – Quasars
• Physics of accretion disks: Self-gravity and viscosity
• The parallel evolution of super-massive black holes and of nuclear (quasar/AGN) activity
Kyoto – 30 October 2003
The three phases of quasar evolution
A numerical example in detail (Duschl & Strittmatter 2003):
• Disk extends from 10-2 to 102 pc
• Initial disk mass: 1010 MSun
• Viscosity parameter : 10-3
• Seed black hole: 103 MSun
• Initial mass distribution ~ s-1
Kyoto – 30 October 2003
The three phases of quasar evolution
Kyoto – 30 October 2003
The three phases of quasar evolution
Kyoto – 30 October 2003
The three phases of quasar evolution
Kyoto – 30 October 2003
The “final” mass of the black hole
Kyoto – 30 October 2003
The evolution time scale
Kyoto – 30 October 2003
The mass flow rate
Kyoto – 30 October 2003
The quasar regime
Kyoto – 30 October 2003
Summary
• Black holes in quasars may be formed as a result of galaxy-galaxy interactions – but it needs a major event, not just a fly-by type of interaction.
• In today‘s Universe there are too few galaxy-galaxy interactions to form many new quasars, and the old ones have used up all their “fuel”.
Kyoto – 30 October 2003
Summary
• It takes only a few 102 million years to form a suitably massive black hole and to switch the quasar on.
• For the subsequent few 102 million years it acts as a “normal” quasar.
• After altogether only ~109 years the quasar phase comes to an end for good (unless ...)
Kyoto – 30 October 2003
Thank you very much
for your attention !