sailfish.physics.circumbinary.PointMass

class sailfish.physics.circumbinary.PointMass(mass: float = 0.0, position_x: float = 0.0, position_y: float = 0.0, velocity_x: float = 0.0, velocity_y: float = 0.0, softening_length: float = 0.0, sink_model: SinkModel = SinkModel.INACTIVE, sink_rate: float = 0.0, sink_radius: float = 0.0)

Bases: NamedTuple

Describes a gravitating point mass

The point mass’s mass, x-y position, and softening length fully determine the gravitational potential:

\[\phi = \frac{G M}{\sqrt{\Delta r^2 + r_{\rm soft}^2}} \, .\]

Here, \(\Delta r\) is the distance from the particle to the field point, and \(r_{\rm soft}\) is the softening_length parameter below. Note that the gravitational constant is assumed to be 1 by the physics solvers.

Point masses can also act as sinks of mass and momentum. This behavior is controlled by the sink model, sink rate, and a sink radius. If the sink model has the value SINK_MODEL_INACTIVE, then that particle may still be a source of gravitational potential, but it does model accretion by subtracting mass or momentum. The acceleration-free and torque-free modes are described in literature here:

• Dittmann & Ryan (2021)

• Dempsey et. al (2020)

The acceleration-free sink model is there for logical completeness, but it should not be used in practice.

__init__()

Methods

__init__()
count(value, /)	Return number of occurrences of value.
index(value[, start, stop])	Return first index of value.

Attributes

mass	The mass (really G * M since solvers assume G = 1)
position_x	The x-position
position_y	The y-position
sink_model	The equation used to control how momentum is subtracted
sink_radius	The sink radius: how far from the particle the sink extends
sink_rate	The sink rate: how fast mass and momentum are removed
softening_length	Gravitational softening length
velocity_x	The x-velocity
velocity_y	The y-velocity

count(value, /)

Return number of occurrences of value.

index(value, start=0, stop=9223372036854775807, /)

Return first index of value.

Raises ValueError if the value is not present.

mass: float

The mass (really G * M since solvers assume G = 1)

position_x: float

The x-position

position_y: float

The y-position

sink_model: SinkModel

The equation used to control how momentum is subtracted

sink_radius: float

The sink radius: how far from the particle the sink extends

sink_rate: float

The sink rate: how fast mass and momentum are removed

softening_length: float

Gravitational softening length

velocity_x: float

The x-velocity

velocity_y: float

The y-velocity