Question about black holes and gravity

[pitoko]

The black hole is surrounded by an event horizon. No matter which fell under the horizon will never escape, even in the form of information (in the classical theory of relativity). So why is the star orbiting a black hole moving at the correct speed and trajectory, as if they knew the mass of a black hole? Knowledge of the mass of the black hole, depends on the amount of matter inside the event horizon, and this is a secret. How nature does it do?

 

[Dale]

Hi pitoko, welcome to PF.

Black holes have charge, angular momentum, and mass. Look up "no hair theorem". It is not clear that the "no hair theorem" is always correct and so black holes may have some more hair, but they certainly have at a minimum the charge, angular momentum, and mass.

 

[bcrowell]

Any observer who was around before the black hole formed know how much mass went in, so the mass can't be secret. The curvature of spacetime surrounding the black hole is a frozen record of how much mass went in. Note that a person inside the event horizon can't use the mass of the black hole to send information to the outside; since the mass is conserved, it's not possible to modulate the signal.

 

[pitoko]

Thank you for your answers DaleSpam and bcrowell, you answered me exactly what I wanted to know ;)