# Presentation: 116031

## Dynamics of Galaxy Cores and Supermassive Black Holes

- David Merritt
- Santa Fe, July 2006

## Nuclear Structure

- Most spheroids* are well fit by Sersic profiles at all radii:

- *Elliptical galaxy, or  bulge of spiral galaxy.

- NGC 4762

## Nuclear Structure

- Bright* spheroids exhibit mass deficits, or *cores*.

- *MV < -21.5

- NGC 4406

## Nuclear Structure

- Bright* spheroids exhibit mass deficits, or *cores*.
- The core radius is ~ the SBH influence radius.
- The core mass is ~ the SBH mass.

- *MV < -21.5

- rcore

- NGC 4406

## Nuclear Structure

- Faint* spheroids exhibit central excesses, or *nuclei*.

- *MV > -18

- NGC 4482

## Nuclear Structure

- Faint* spheroids exhibit central excesses, or *nuclei*.
- The nuclear luminosity is ~10-3.5 times the total luminosity.
- The nucleus is typically unresolved.

- *MV > -18

- NGC 4482

## Nuclear relaxation times show a clear dependence on spheroid luminosity.

- “Most” nuclei are *collisionless,* i._x001a_e. TR >> 1010 yr.

- 16 Gyr

## Nuclear relaxation times show a clear dependence on spheroid luminosity.

- The structure of bright spheroids should still reflect the details of their formation.

- core

## Nuclear relaxation times show a clear dependence on spheroid luminosity.

- The structure of faint spheroids should correspond to “collisional” states.

## Bahcall-Wolf Solution

- Two-body encounters lead to a redistribution of stars in energy space:

## Bahcall-Wolf Solution

- Two-body encounters lead to a redistribution of stars in energy space:

- The most relevant solution is *F**E*= 0 (“zero flux”), which implies, in the potential of the BH:

- The exact solution has *F**E *≈ 0; the flux is limited by the rate at which stars diffuse into the black hole.

## Elapsed time ~ 1 TR

- Elapsed time ~ 1 *T**R*

## Radius of cusp  ~ 0.2 rh

- ~0.2*r**h*

- Radius of cusp  ~ 0.2 *r**h*

## The Galactic center star cluster has a density profile that is consistent with the Bahcall-Wolf form, though perhaps shallower.

- 0.2*r**h*

- Schödel et al. 2006

## In fact, loss of stars into the black hole is dominated by changes in J, not E.

- Write this loss term as *F**J*(*E*).  Then:

## In fact, loss of stars into the black hole is dominated by changes in J, not E.

- Write this loss term as *F**J*(*E*).  Then:

*F**J*(*E*) is “large”, in the sense that a mass ~*M*BH should be scattered into the black hole in a time ~*T**R*.

## Stellar Disruption Rates

- Wang & Merritt 2004

## In fact, loss of stars into the black hole is dominated by changes in J, not E.

- Write this loss term as *F**J*(*E*).  Then:

- and a steady state requires:

- i.e. the loss ∫*F**J **dE *into the black hole must be balanced by “downward” diffusion in energy.

## Nuclear Expansion due to a Black Hole

- ~M32

## Nuclear Expansion due to a Black Hole

- Multi-Mass Evolution

## Massive remnants/stellar-mass BHs

- Massive remnants/stellar-mass BHs

- Low-mass (observed) stars

## Observed stars

- Particle dark matter

## Graham 2004

- core

## Observed Mass Deficits

## Observed Mass Deficits

- Mdef ≈ 1 MBH

## An inspiralling black hole displaces stars.

- Ebisuzaki, Makino & Okumura 1991

## An inspiralling black hole displaces stars.

- Lagrange radii

## An inspiralling black hole displaces stars.

- Separations

- 1:2

- 1:40

- astro-ph/0603439

## astro-ph/0603439

## astro-ph/0603439

## i. e. Mdef ≈ 0.5(m1+m2)

- i. e. *M*def ≈ 0.5(m1+m2)

- astro-ph/0603439

## But, mass deficits are cumulative:Mdef ≈ 0.5NmergeMBH,

- But, mass deficits are *cumulative*:*M*def ≈ 0.5Nmerge*M**BH*,

- 1:2

- 1:10

- astro-ph/0603439

## But, mass deficits are cumulative:Mdef ≈ 0.5NmergeMBH,

- But, mass deficits are *cumulative*:*M*def ≈ 0.5Nmerge*M**BH*,
- i.e. observed mass deficits are consistent with bright E-galaxies having experienced 2-3 “dry” mergers since black hole formation.

- 1:2

- 1:10

- astro-ph/0603439

## The observed (projected) separation of ~7 pc is the expected stalling radius for a ~109 Msun black hole.

- Rodriguez et al. 2006

## Core formation by binary SBHs removes the need for “two families” of elliptical galaxies

- (Kormendy 1985).

## Core formation by binary SBHs removes the need for “two families” of elliptical galaxies

- (Kormendy 1985).

## Bright galaxies once had higher central densities/surface brightnesses.

- (Jerjen & Binggeli 1997, Graham & Guzman 2003)

## In a collisional nucleus like that of the Milky Way, a density cusp can regenerate after being destroyed by a binary black hole.

- In a collisional nucleus like that of the Milky Way, a density cusp can regenerate after being destroyed by a binary black hole.

## Orbit families in triaxial potentials.

- Orbit families in triaxial potentials.

- Poon 2002

## Binary evolution in spherical galaxy.

- Binary evolution in spherical galaxy.

- Binary evolution in triaxial galaxy.

- Berczik et al. 2006

## Berczik et al. 2006

## Triple (Multiple) Black Holes

- Harfst & Bischof 2006

## Slide 43