The Bondi radius is a calculated radius of the region surrounding an astronomical object from which surrounding medium (gas, dust) is likely to be drawn in and accreted. It includes the effects of the (relative) speed of the object through the medium, and the medium's density and sound-speed. Accretion due to such material falling from within the Bondi radius is termed Bondi accretion. The Bondi radius calculation was developed modeling the accretion by a compact object (black hole or neutron star) of the medium it is passing through. The concept has since been applied to planet formation, i.e., protoplanets passing through the material of a protoplanetary disk.