# Massive Black Hole Physics Parameters¶

Following parameters are for the accretion and feedback from the massive black hole particle (PARTICLE_TYPE_MBH). Details are described in Kim, Wise, Alvarez, and Abel (2011).

## Accretion Physics¶

MBHAccretion (external)
Set to 1 to turn on accretion based on the Eddington-limited spherical Bondi-Hoyle formula (Bondi 1952). Set to 2 to turn on accretion based on the Bondi-Hoyle formula but with fixed temperature defined below. Set to 3 to turn on accretion with a fixed rate defined below. Set to 4 to to turn on accretion based on the Eddington-limited spherical Bondi-Hoyle formula, but without v_rel in the denominator. Set to 5 to turn on accretion based on Krumholz et al.(2006) which takes vorticity into account. Set to 6 to turn on alpha disk formalism based on DeBuhr et al.(2010). 7 and 8 are still failed experiment. Add 10 to each of these options (i.e. 11, 12, 13, 14) to ignore the Eddington limit. See Star_CalculateMassAccretion.C. Default: 0 (FALSE)
This is the radius (in pc) of a gas sphere from which the accreting mass is subtracted out at every timestep. Instead, you may want to try set this parameter to -1, in which case an approximate Bondi radius is calculated and used (from DEFAULT_MU and MBHAccretionFixedTemperature). If set to -N, it will use N*(Bondi radius). See CalculateSubtractionParameters.C. Default: 50.0
MBHAccretingMassRatio (external)
There are three different scenarios you can utilize this parameter. (1) In principle this parameter is a nondimensional factor multiplied to the Bondi-Hoyle accretion rate; so 1.0 should give the plain Bondi rate. (2) However, if the Bondi radius is resolved around the MBH, the local density used to calculate Mdot can be higher than what was supposed to be used (density at the Bondi radius!), resulting in the overestimation of Mdot. 0.0 < MBHAccretingMassRatio < 1.0 can be used to fix this. (3) Or, one might try using the density profile of R-1.5 to estimate the density at the Bondi radius, which is utilized when MBHAccretingMassRatio is set to -1. See Star_CalculateMassAccretion.C. Default: 1.0
MBHAccretionFixedTemperature (external)
This parameter (in K) is used when MBHAccretion = 2. A fixed gas temperature that goes into the Bondi-Hoyle accretion rate estimation formula. Default: 3e5
MBHAccretionFixedRate (external)
This parameter (in Msun/yr) is used when MBHAccretion = 3. Default: 1e-3
MBHTurnOffStarFormation (external)
Set to 1 to turn off star formation (only for StarParicleCreation method 7) in the cells where MBH particles reside. Default: 0 (FALSE)
The distance (in pc) between two MBH particles in which two energetically-bound MBH particles merge to form one particle. Default: 50.0
MBHMinDynamicalTime (external)
Minimum dynamical time (in yr) for a MBH particle. Default: 1e7
MBHMinimumMass (external)
Minimum mass (in Msun) for a MBH particle. Default: 1e3

## Feedback Physics¶

MBHFeedback (external)
Set to 1 to turn on thermal feedback of MBH particles (MBH_THERMAL - not fully tested). Set to 2 to turn on mechanical feedback of MBH particles (MBH_JETS, bipolar jets along the total angular momentum of gas accreted onto the MBH particle so far). Set to 3 to turn on another version of mechanical feedback of MBH particles (MBH_JETS, always directed along z-axis). Set to 4 to turn on experimental version of mechanical feedback (MBH_JETS, bipolar jets along the total angular momentum of gas accreted onto the MBH particle so far + 10 degree random noise). Set to 5 to turn on experimental version of mechanical feedback (MBH_JETS, launched at random direction). Note that, even when this parameter is set to 0, MBH particles still can be radiation sources if RadiativeTransfer is on. See Grid_AddFeedbackSphere.C. Default: 0 (FALSE)
`````RadiativeTransfer = 0`` & ``MBHFeedback = 0`` : no feedback at all
``RadiativeTransfer = 0`` & ``MBHFeedback = 1`` : purely thermal feedback
``RadiativeTransfer = 0`` & ``MBHFeedback = 2`` : purely mechanical feedback
mechanical feedback combined (one has to change the following
``MBHFeedbackRadiativeEfficiency`` parameter accordingly, say from 0.1
to 0.05, to keep the same total energy across different modes of
feedback)
```
The radiative efficiency of a black hole. 10% is the widely accepted value for the conversion rate from the rest-mass energy of the accreting material to the feedback energy, at the innermost stable orbit of a non-spinning Schwarzschild black hole (Shakura & Sunyaev 1973, Booth & Schaye 2009). Default: 0.1
MBHFeedbackEnergyCoupling (external)
The fraction of feedback energy that is thermodynamically (for MBH_THERMAL) or mechanically (for MBH_JETS) coupled to the gas. 0.05 is widely used for thermal feedback (Springel et al. 2005, Di Matteo et al. 2005), whereas 0.0001 or less is recommended for mechanical feedback depending on the resolution of the simulation (Ciotti et al. 2009). Default: 0.05
MBHFeedbackMassEjectionFraction (external)
The fraction of accreting mass that is returning to the gas phase. For either MBH_THERMAL or MBH_JETS. Default: 0.1
MBHFeedbackMetalYield (external)
The mass fraction of metal in the ejected mass. Default: 0.02