This is the expression for both, but some authors use one name and it has confused me. Is there any distinction?


The Bondi radius is $2MG/s^2$ where M is the mass, G is the gravitational constant and $s$ is the speed of sound in the medium of the accretion disk. It represents the boundary between sub-sonic and super-sonic infall of matter into the black hole.

The Schwartzchild radius is $2MG/c^2$ where $c$ is the speed of light and is the radius of the event horizon.

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    $\begingroup$ The OP's error possibly derives from the Wikipedia page, which gives the denominator in the expression as $c_{s}^{2}$ where $c_{s}$ is defined as the sound speed in the surrounding medium. A good lesson in paying attention to subscripts ;-) $\endgroup$ – Chappo Jan 2 at 0:39

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