# Black hole gravitational question

• LoveKnowledge
In summary, the conversation discusses the gravitational force of a black hole and how it increases as the black hole consumes more matter. The conversation also clarifies that a black hole retains the properties of the matter it consumes, such as mass, angular momentum, and electric charge. The only difference between a black hole and a star is that the pull of a black hole is stronger due to its smaller size. The conversation ends with a question about the Schwarzschild radius of different sized black holes, which is explained by the formula r = 2GM/c^2.
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"?

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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 :)

## 1. 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 it. This occurs when a massive star collapses in on itself, creating a singularity with infinite density and zero volume.

## 2. How is a black hole's gravitational pull measured?

The strength of a black hole's gravitational pull is measured by its event horizon, which is the point of no return for anything that crosses it. The larger the event horizon, the stronger the gravitational pull.

## 3. Can anything escape a black hole's gravitational pull?

No, once something crosses the event horizon of a black hole, it is impossible for it to escape. The only way for something to escape a black hole's pull is if it has not yet reached the event horizon.

## 4. Do black holes have an effect on time?

Yes, black holes have a strong effect on time due to their immense gravitational pull. Time near a black hole passes slower than time in other regions of space, a concept known as time dilation.

## 5. Can we observe black holes directly?

No, we cannot observe black holes directly because their gravitational pull is so strong that not even light can escape it. However, we can detect their presence through the effects they have on nearby matter and light.

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