.. _physics-blackHoleAccretionRate:

Black Hole Accretion Rates
==========================

Class providing models of the mass accretion rates onto supermassive black holes from the spheroid, hot halo, and nuclear star cluster components. Accretion drives black hole growth and AGN feedback. Implementations typically adopt Bondi-type formulae, Eddington-limited accretion, or empirical models that parameterize the accretion rate as a function of the available gas supply and the potential well depth.

**Default implementation:** ``blackHoleAccretionRateStandard``

Methods
-------

``rateAccretion`` → ``void``
   Computes the mass accretion rate onto a black hole from the spheroid, hot halo, and nuclear star cluster components, returning each contribution separately (in :math:`\mathrm{M}_\odot` Gyr\ :math:`^{-1}`).

   * ``class (nodeComponentBlackHole), intent(inout) :: blackHole``

   * ``double precision , intent( out) :: rateMassAccretionSpheroid, rateMassAccretionHotHalo, rateMassAccretionNuclearStarCluster``

.. _physics-blackHoleAccretionRateSpheroidTracking:

``blackHoleAccretionRateSpheroidTracking``
------------------------------------------

A black hole accretion rate class that drives black hole growth in proportion to the stellar mass growth rate of the host spheroid. The ratio of black hole growth to spheroid stellar mass growth is set by the ``[growthRatioToStellarSpheroid]`` parameter.

**Parameters**

* ``[growthRatioToStellarSpheroid]`` (real; default ``1.0d-3``) — The ratio of the rates of black hole growth and spheroid stellar mass growth.

.. _physics-blackHoleAccretionRateStandard:

``blackHoleAccretionRateStandard``
----------------------------------

Computes black hole accretion rates via Bondi-Hoyle accretion from spheroid gas, hot halo gas, and nuclear star cluster gas. Enhancement factors above the classical Bondi rate are set independently via ``[bondiHoyleAccretionEnhancementSpheroid]``, ``[bondiHoyleAccretionEnhancementHotHalo]``, and ``[bondiHoyleAccretionEnhancementNuclearStarCluster]``. The gas temperature assumed for each component and whether to restrict hot halo accretion to the hot-mode only are also configurable.

**(Default implementation)**

**Methods**

* ``factors`` — Compute factors needed for tidal tensor calculation.
* ``tidalTensorGet`` — Get the tidal tensor.

**Parameters**

* ``[bondiHoyleAccretionEnhancementSpheroid]`` (real; default ``5.0d0``) — The factor by which the Bondi-Hoyle accretion rate of spheroid gas onto black holes is enhanced.
* ``[bondiHoyleAccretionEnhancementHotHalo]`` (real; default ``6.0d0``) — The factor by which the Bondi-Hoyle accretion rate of hot halo gas onto black holes is enhanced.
* ``[bondiHoyleAccretionEnhancementNuclearStarCluster]`` (real; default ``5.0d0``) — The factor by which the Bondi-Hoyle accretion rate of :term:`NSC` gas onto black holes is enhanced.
* ``[bondiHoyleAccretionHotModeOnly]`` (boolean; default ``.true.``) — Determines whether accretion from the hot halo should only occur if the halo is in the hot accretion mode.
* ``[bondiHoyleAccretionTemperatureSpheroid]`` (real; default ``1.0d2``) — The assumed temperature (in Kelvin) of gas in the spheroid when computing Bondi-Hoyle accretion rates onto black holes.
* ``[bondiHoyleAccretionTemperatureNuclearStarCluster]`` (real; default ``1.0d2``) — The assumed temperature (in Kelvin) of gas in the :term:`NSC` when computing Bondi-Hoyle accretion rates onto black holes.