Bondi accretion
Bondi accretion is spherical accretion onto an object. It is generally used in the context of neutron star and black hole accretion for a compact object traveling through the interstellar medium. It is named after Hermann Bondi.
To achieve an approximate form of the Bondi accretion rate, accretion is assumed to occur at a rate
\dot{M} = \pi R^2 \rho v
where \rho is the ambient density, v is either the velocity of the object or the sound speed c_s in the surrounding medium if the object's velocity is lower than the sound speed, and the radius R provides an effective area. The effective radius is acquired by equating the object's escape velocity and the relevant speed, i.e.
\sqrt{\frac{2 G M}{R}} = c_s
or
R=\frac{2 G M}{c_s^2} .
The accretion rate therefore becomes
\dot{M} = \frac{4 \pi \rho G^2 M^2 }{c_s^3} .
This derivation is only approximate, using scaling relations rather than rigorous definitions. A more complete solution can be found in Bondi's original work and two other papers.
Bibliography
 Bondi (1952) MNRAS 112, 195, link
 Mestel (1954) MNRAS 114, 437
 Hoyle and Lyttleton (1941) MNRAS 101, 227
References
