Question about black holes and gravity

In summary, the conversation discusses the concept of a black hole and how its mass affects the orbit of surrounding stars. It is mentioned that black holes have charge, angular momentum, and mass, and the "no hair theorem" states that their mass depends on the amount of matter inside the event horizon. This information is not accessible to observers outside the black hole, but the curvature of spacetime surrounding it can provide a record of its mass.
  • #1
pitoko
2
0
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?
 
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  • #2
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.
 
  • #3
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.
 
  • #4
Thank you for your answers DaleSpam and bcrowell, you answered me exactly what I wanted to know ;)
 

What is a black hole?

A black hole is a region in space where the gravitational pull is so strong that nothing, including light, can escape from it. It is formed when a massive star dies and its core collapses under its own gravity.

How does gravity work in a black hole?

In a black hole, the gravity is so strong because the mass is concentrated in an extremely small space. The more mass a black hole has, the stronger its gravitational pull will be.

Can anything escape from a black hole?

No, once an object crosses the event horizon of a black hole (the point of no return), it is pulled into the black hole and cannot escape. However, some particles can escape from the edges of the black hole due to the phenomenon of Hawking radiation.

What is the relationship between black holes and time?

The extreme gravitational pull of a black hole has a strong impact on time. Time slows down near the event horizon of a black hole and stops completely at the singularity (the center of the black hole).

Do black holes have an impact on the universe?

Yes, black holes play a crucial role in the formation and evolution of galaxies. They are also responsible for the gravitational lensing effect, where the path of light is bent by the strong gravity of a black hole.

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