The horizon radius r_{H} is equal to 2 M G divided by c^{2}. This is equal to about 2.9 km times the mass of the black hole as measured in solar masses.

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1. Robert McNees (mcnees@mastodon.social)'s status on Sunday, 08-Jan-2023 20:22:33 UTC Robert McNees

   in reply to

   To get a feel for how this works for astrophysical black holes, let's look at the simplest case: Schwarzschild's non-rotating black hole.

   In that case the radius of the horizon is proportional to the mass of the black hole.

   Here G is Newton's constant and c is the speed of light. A solar-mass black hole has a Schwarzschild radius of around 3 km. But our sun isn't massive enough to form a black hole. A more massive star that became a 20 solar mass black hole would have a radius of ~59 km.