Light and black holes

[billasker]

In school our teacher said that black holes have such a huge gravitational pull that not even the light can escape it.I asked him how since the light has no mass.He said that photons actually do have a mass but only if they are not moving and he showed us Einstein's equasion about mass and velocity: m=m_o/(square root)1-V/c .How is that even possible?

 

Sorry about any mistakes and about that square root thing but I'm using my phone and there is no square root on the keyboard

[mathematic]

Your teacher's explanation is not very good.  Photons always move (in a vacuum) at the speed of light, never at 0 speed.  The simplest explanation for for light not escaping is the equivalence between mass and energy (which light has), both subject to the effect of gravity.  The formula he was using E=mc^2/sqrt(1-(v/c)^2)shows the relationship between mass and energy, where the rest mass is m, v is the speed of the particle, and c is the speed of light.  Note:  there are more recent versions in terms of momentum.

Edited February 12, 2018 by mathematic
latex ????

[beecee]

4 hours ago, billasker said:

In school our teacher said that black holes have such a huge gravitational pull that not even the light can escape it.I asked him how since the light has no mass.He said that photons actually do have a mass but only if they are not moving and he showed us Einstein's equasion about mass and velocity: m=m_o/(square root)1-V/c .How is that even possible?

 

Sorry about any mistakes and about that square root thing but I'm using my phone and there is no square root on the keyboard

Light does not have any measurable rest mass, but due to its speed, it does have momentum...that's why solar sails work as an example.

Also light/photons travel in geodesic paths in spacetime:  The curvature at the EH of a BH is such that light simply has no choice in the geodesic path it must travel, which is to the singularity.