Black hole mass question

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1. Apr 30, 2015

Mohan Nivas

How the black hole acquire greater mass than any other objects in the universe...?

2. Apr 30, 2015

Staff Emeritus
They don't.

3. Apr 30, 2015

Mohan Nivas

Are u saying they don't have mass...?

4. Apr 30, 2015

phinds

That's ridiculous. He is saying they don't have greater mass than any other objects in the universe, as a direct answer to your question.

I'd be more likely to say that for a given size, they have more mass than anything else, but there are small black holes that have much less mass than some huge stars.

Again, I caution you against just asking random questions on an internet forum. Read some books and then ask questions if you don't undertstand. CLEARLY your level of understanding right now is such that asking random questions on an internet is NOT the best way for you to learn.

5. Apr 30, 2015

DaveC426913

Mohan, a black hole might be no more massive than our sun (though this is not the natural progression of our sun). The key to a black hole's strong gravity is that, because of its size, you can get much closer to it than a normal object.

The gravitational force experienced near the sun (or any object) is a product of its mass and the square of the distance to its centre.

The sun is 400,000 miles in radius. The closest you can get to it is 400,000 miles from its centre. That is where you will experience the highest gravitational force: 28g's.

But if the sun were to turn into a black hole, it would shrink to being only 2 miles in radius. While its mass would not change at all, you could now get 399,998 miles closer to the centre of that mass. You would now experience a gravitational force that is (399,998/2)2 times larger.

Note that this would have NO effect on the planets of the solar system. They are still the same distance from the same mass. The sun's gravitational influence on the planets has not changed at all.

Last edited: Apr 30, 2015
6. Apr 30, 2015

Mohan Nivas

Oh... So their mass is not much but have stronger gravitational pull than stars having same mass isn't it...?

7. Apr 30, 2015

wabbit

No, they have exactly the same gravitational pull as a star of the same mass. Re-read the answer you quoted.

8. Apr 30, 2015

DaveC426913

At the same distance, they have exactly the same pull. Mercury will not notice if the Sun suddenly collapses to form a BH.
But you could get closer to it (say, by diving into the sun's vicinity in a spaceship), which means you will experience a stronger force there.

9. Apr 30, 2015

Mohan Nivas

Then how black hole attracts light while stars don't...?
Stars only can bend the light rays but black hole attracts the light..
I am getting confused can you clear it..?

10. Apr 30, 2015

DaveC426913

Black holes do not "attract" light.
They bend light exactly the same way stars do. But because their gravity is so huge, light passing very close is bent directly toward the BH, so that it cannot escape.

11. Apr 30, 2015

Mohan Nivas

oh...
I had heard that they can eat stars how it happen...?

12. Apr 30, 2015

Staff: Mentor

You will find the Physics Forums rules here;they include a section on acceptable sources, and "I had heard" is not one of them. Please find and study a decent textbook or other serious source. Then when you have specific questions based on that study come back and ask, and we can help you work through them; but throwing random questions into an internet forum is just a waste of everyone's time.