Astronomy & Space
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Photon Sphere Radius

Radius where gravity bends light into a circular orbit.

Formula

rph=3GMc2r_{ph} = \frac{3GM}{c^2}

Variables

GGravitational constant
MMass
cSpeed of light

Example

It sits at 1.5 times the Schwarzschild radius

Did You Know?

At the photon sphere, in principle you could see the back of your own head as light loops around the black hole.

black holelightorbit