In astrophysics, the Bondi accretion (also called Bondi-Hoyle-Lyttleton Accretion), named after Hermann Bondi, is spherical accretion onto a compact object traveling through the interstellar medium. It is generally used in the context of neutron star and black hole accretion. To achieve an approximate form of the Bondi accretion rate, accretion is assumed to occur at a rate . Where: * is the ambient density * is the object's velocity or the sound speed in the surrounding medium if * is the Bondi radius, defined as . .