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: L : Luminosity M a : accreting mass M : mass flow rate pot : potential energy r (r min ) : (inner) radius accretion efficiency. Fan et al. (2003; SDSS): z = 6.4 Then the Universe was 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 10 2 pc (observations: Sanders et al …; models: e.g., Barnes & Hernquist 1996, 1999; Barnes 2002 …), until – because of the angular momentum – it gets stuck at some 10 2 pc. Subsequently, accretion – hopefully – allows to bridge the last few 10 2 pc, and to do so quickly (within less than 10 9 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 rate g r, g s, g z gravitational acceleration in r, s und z direction v s, v velocity in s und direction angular velocity in direction M * mass of accretor s a outer disk radius s i inner disk radius density surface density h thickness of disk T temperature c S sound velocity viscosity time scales Reynolds number {s, , z; t} cylindrical coordinate system r 2 = s 2 + z 2 vv vsvs M *, s i sasa s z
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: Relevant time scales: - dynamical - viscous
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: *: In NSG disks Shakura & Sunyaev´s a parameterization has proven to be very successful: = h c s
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.
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)
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 to 10 2 pc Initial disk mass: M Sun Viscosity parameter : Seed black hole: 10 3 M Sun 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 10 2 million years to form a suitably massive black hole and to switch the quasar on. For the subsequent few 10 2 million years it acts as a “normal” quasar. After altogether only ~10 9 years the quasar phase comes to an end for good (unless...)
Kyoto – 30 October 2003 Thank you very much for your attention !