Black hole gravitational question

[LoveKnowledge]

Hi all! This is not a problem for my homework. It is just something I was reading in my textbook and wanted a little clarification.

According to my textbook, the gravitation force of a black hole is the same as the original fields about the stars before collapse...but doesn't a black holes gravitational force increase as it is eating up more matter and stars...doesn't it get bigger as it accumulates more "stuff"?

 

[LoveKnowledge]

To note: I also say this is because a black hole does retain mass, angular momentum, and electric charge of what it eats so I would think the gravitational force would increase as well..

 

[Drakkith]

Yes, it will grow bigger as it "eats" stuff.
Your book is probably saying its the same as the star right after collapse.

 

[Danger]

Roger that. All of the angular momentum, electric and magnetic fields, and mass are conserved within the hole (excepting that which is ejected from the star during the formation thereof). If our sun were to turn into a black hole (impossible, by the bye, since it requires 3.2 solar masses), the orbits of the planets would not be affected at all. Same mass, same place. We would continue to orbit in darkness and frigid cold.

 

[DaveC426913]

The gravitational pull from a black hole is dependent only on its mass. Whether that mass is as big as a star or as tiny as a BH makes no difference.

IF a massive object (be it BH or star) consumes infalling matter, its gravitational force will grow.

The only difference between a BH and a star is that, since the BH is very tiny, you can get much closer to it, and that's where the pull is stronger.

 

[LoveKnowledge]

thx for the clarification :)

 

[LoveKnowledge]

One last thing...I am a little confused.

Why does the Schwarzschild radius of a 10-solar mass black hole be only 3-times larger than a 3-solar mass black hole? I am just doing a review tutorial and this confuses me...it is 7-solar mass more..

 

[Chronos]

The Schwarzschild radius is given by the expression r = 2GM/c^2, where G is the gravitational constant and M is mass. So 10 solar masses produces a radius ~3 times larger than 3 solor masses.

 

[LoveKnowledge]

thx :)