Black hole gravitational question

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Discussion Overview

The discussion revolves around the gravitational properties of black holes, particularly how their gravitational force changes as they accumulate mass. Participants explore concepts related to gravitational force, mass retention, and the Schwarzschild radius in the context of black holes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants propose that a black hole's gravitational force is equivalent to that of the original star before its collapse, while others argue that it increases as the black hole consumes more matter.
  • It is noted that a black hole retains mass, angular momentum, and electric charge from the matter it consumes, suggesting that its gravitational force would increase accordingly.
  • One participant clarifies that the gravitational pull from a black hole depends solely on its mass, and that consuming infalling matter will increase its gravitational force.
  • Another participant mentions that if the sun were to become a black hole, the gravitational effects on the orbits of the planets would remain unchanged, as the mass would be conserved.
  • A participant expresses confusion regarding the relationship between mass and Schwarzschild radius, specifically why a 10-solar mass black hole has a radius only three times larger than a 3-solar mass black hole.
  • The formula for the Schwarzschild radius is provided, indicating that it scales with mass, but the implications of this scaling are not fully resolved in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on how gravitational force relates to mass accumulation in black holes, with some asserting that it increases while others reference the gravitational equivalence to the original star's mass. The discussion on the Schwarzschild radius also indicates some confusion and lack of consensus on the implications of mass scaling.

Contextual Notes

There are unresolved questions regarding the implications of mass conservation and gravitational force in black holes, as well as the specific scaling of the Schwarzschild radius in relation to mass. Participants do not fully clarify these points, leaving some assumptions and definitions unaddressed.

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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"?
 
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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..
 
Yes, it will grow bigger as it "eats" stuff.
Your book is probably saying its the same as the star right after collapse.
 
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.
 
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.
 
thx for the clarification :)
 
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..
 
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.
 
thx :)
 

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