Question

Monica and Dylan are doing a “thought experiment”. They are imagining that Monica is in a space ship orbiting a black hole, just outside the event horizon, while Dylan is in a space ship 1 light year away. Monica and Dylan each send each other a signal using a laser. From each of their perspectives, their laser flashes once a second. To Dylan, is Monica’s laser flashing faster, slower or at the same rate (once a second)? Similarly, how fast does Dylan’s laser appear to be flashing from Monica’s point of view?

Answer 1

Considering the mentioned Scenario,I would like to make a few more considerations.Monica's space ship is outside of event horizon and photon sphere present around the black hole.

Light cannot escape from a Black Hole if it comes from a radius closer than the Schwarzschild Radius,Rs

Rs=2GM/c^2

Where M = Mass of the Black Hole,c=speed of light.

Let us consider Distance of Monica from Black hole as R

When Monica flashes a perfectly radial light towards Dylan every Second,For Dylan the light flashes at increased time intervals and the flash light has become more redder.As we Know

Energy of a photon=hc/λ where λ is wavelength,c is speed,h is planck's constant .

Since Huge Gravity around black hole decreases light energy but the light speed remains constant,hence the wavelength increases.Also due to gravity the light is warped and takes longer to reach Dylan,hence time interval between flashes increase.

We will observe similar results as mentioned,When Dylan flashes light towards Monica.