my sur said asked this and said earth won't fall in then i had an debate with him on him but he still says earth wont fall

he is an IITan and an physics expert so war he right or wrong?

He's right it wouldn't. Same gravity would be felt at the Earth.

 

Mass is the same so the gravity is the same. It is only inside the hole that you'd notice the difference(perpetual darkness not withstanding).

but i heard that even light cant escape its gravity so why wont earth fall in ??

Light that is within the event horizon of the black hole cannot escape. The event horizon would be near what is now the center of the sun. The extreme gravity of a black hole is not experienced until you are very near it.

Light that is within the event horizon of the black hole cannot escape. The event horizon would be near what is now the center of the sun. The extreme gravity of a black hole is not experienced until you are very near it.

but earth will be near to it

but earth will be near to it

 

Distance between Earth and Sun is ~150 mln km..

but then black hole's gravity is huge

At earth's current distance the earth will continue to orbit. Doesn't matter if the sun turns into a black hole or if the diameter increased 10 fold. The gravitational pull on earth will remain the same.

ok so he was right

If the sun turned into a black hole as you said in your original post, then the mass would remain the same. If it the same mass, it is the same gravitational pull. That is why there would be no impact on the earth.

 

Yes, he was right.

Edited January 13, 201411 yr by zapatos

If the sun turned into a black hole as you said in your original post, then the mass would remain the same. If it the same mass, it is the same gravitational pull. That is why there would be no impact on the earth.

 

Yes, he was right.

i thought that its gravity increase because its an black hole

If you have star with initial mass m, after burning out all fuel and collapse it's mass is smaller than initial m. During lifetime star is ejecting clouds of gas/plasma in eruptions.

Gravity increases as you get nearer the center of mass. On the surface of the sun you will feel the greatest gravitational pull. If you move as far from the sun as the earth is, the gravity will be less because you are further from the center of mass. If you burrow into the sun, the gravity will be less because now some of the mass is over you head. But if the sun shrinks, then you can still be on the surface, but also get closer to the center of mass.

 

The gravity doesn't increase if it turns into a black hole. It increases if you get closer to the center of mass. A black hole is just so small that you can get VERY close to its center of mass.

If you have star with initial mass m, after burning out all fuel and collapse it's mass is smaller than initial m. During lifetime star is ejecting clouds of gas/plasma in eruptions.

can u explain please

 

Gravity increases as you get nearer the center of mass. On the surface of the sun you will feel the greatest gravitational pull. If you move as far from the sun as the earth is, the gravity will be less because you are further from the center of mass. If you burrow into the sun, the gravity will be less because now some of the mass is over you head. But if the sun shrinks, then you can still be on the surface, but also get closer to the center of mass.

 

The gravity doesn't increase if it turns into a black hole. It increases if you get closer to the center of mass. A black hole is just so small that you can get VERY close to its center of mass.

means not even mercury?

Nothing that is above the surface of the sun will notice if the sun turns into a black hole.

 

On the other hand, if a comet comes along and passes closer to the black hole than what was previously the surface of the sun, the comet will experience a stronger gravitational field.

Edited January 13, 201411 yr by zapatos

ookk so i m very wrong indeed

The event horizon, the point where not even light can escape, is only 18 km.

I do not think our sun is actually large enough to become a black hole. I think it would become a white dwarf. However losing our sun would kill us.

thats a point

so what can i conclude?

so what can i conclude?

 

1. The Sun is not going to become a black hole.

 

2. If it did, there would be no change in the Earth's orbit.

Nothing that is above the surface of the sun will notice if the sun turns into a black hole.

 

I understand that gravity isn't a "sucking" force, but I often think of the increase in gravity near the event horizon of a black hole as being like the end of the hose on a vacuum cleaner. The force pushing something towards the hole at the end of the hose isn't really felt until you get very close, and then it becomes irresistible to anything without the mass to beat it. Is that an accurate way to look at it (as far as analogy ever goes)?

 

1. The Sun is not going to become a black hole.

 

2. If it did, there would be no change in the Earth's orbit.

thnx for conclusion sir

 

I understand that gravity isn't a "sucking" force, but I often think of the increase in gravity near the event horizon of a black hole as being like the end of the hose on a vacuum cleaner. The force pushing something towards the hole at the end of the hose isn't really felt until you get very close, and then it becomes irresistible to anything without the mass to beat it. Is that an accurate way to look at it (as far as analogy ever goes)?

 

I think it's a great analogy. There is a lot of confusion about how the gravity of a black hole really affects those things around it.

 

The only part I'm not sure about is when you said 'without the mass to beat it'. The way I always thought of it was that as you approached the event horizon, the only way to avoid crossing over was if you had sufficient velocity. Even two black holes will combine if their velocity does not allow them to pass by or orbit each other.

 

The only part I'm not sure about is when you said 'without the mass to beat it'. The way I always thought of it was that as you approached the event horizon, the only way to avoid crossing over was if you had sufficient velocity. Even two black holes will combine if their velocity does not allow them to pass by or orbit each other.

 

In my analogy, there are things that have more mass than the force from the end of the vacuum hose can overcome, such as my couch. We can assume that if the sun became a black hole, nothing that massive would exist to overcome the force of the gravity at the event horizon. Does that make sense?

 

In my analogy, there are things that have more mass than the force from the end of the vacuum hose can overcome, such as my couch. We can assume that if the sun became a black hole, nothing that massive would exist to overcome the force of the gravity at the event horizon. Does that make sense?

 

If you want a vacuum / sucking analogy I would think of it more as those swimming pool filter pumps - swim past one and you wouldn't notice it - that's us compared to the sun; put your hand near the protective cage / mesh and you will feel the pull but you can still resist - that's close to a star/black hole; but remove the cage or put your hand over the hole and you have got too close and it will drag your hand in and nothing will get it out whilst that pump is on - that's being within the schwarzchild radius. Being in the dangerous position isn't possible with the sun - you have to be well inside the hot bit to be close but once that is a black hole you can get close enough that there is a real problem