(See: Bondi accretion)

Bondi also contributed to the theory of accretion of matter from a cloud of gas onto a star or a black hole, working with Raymond Lyttleton and giving his name to "Bondi accretion" and the "Bondi radius".

Geoffrey R. Burbidge, a research professor of physics at the University of California, San Diego, said Sir Hermann's later work led to a concept known as Bondi accretion, which describes how X-rays can be produced by gas falling from one star to another.

To achieve an approximate form of the Bondi accretion rate, accretion is assumed to occur at a rate where is the ambient density, is either the velocity of the object or the sound speed in the surrounding medium if the object's velocity is lower than the sound speed, and the radius provides an effective area.