Replace sun with a black-hole!

**havaliza** · Nov4-09, 06:42 AM

plz help me to answer to this problem:

Problem: Imagine that we replace sun with a black-hole of same mass.
1. How would be movement of earth?
2. Does the atmosphere of earth change? If yes, explain.

thnx

**Born2bwire** · Nov4-09, 06:46 AM

What are the relevant equations here?

**russ_watters** · Nov4-09, 06:47 AM

From a standpoint of the gravitational effects, nothing on earth would change. From the standpoint of the sun's thermal energy, the earth would quickly freeze.

**havaliza** · Nov4-09, 09:36 AM

You mean that earth will continue it's regular movement around the earth?
I was thinking that earth would straightly go into the black-hole, wouldn't it?
Could you explain a little bit more, plz.

**DaveC426913** · Nov4-09, 09:41 AM

Originally Posted by havaliza

You mean that earth will continue it's regular movement around the earth?
I was thinking that earth would straightly go into the black-hole, wouldn't it?
Could you explain a little bit more, plz.

Gravity depends on one thing and one thing only: the mass.

Since you've replaced the sun with an equivalent mass - regardless of what that mass is - the gravitational force will not change.

Black holes do not have any more gravitational pull than any other object of an equivalent mass. What's unique about black holes is that you can get much closer to them, which is where gravity gets very strong.

**havaliza** · Nov4-09, 10:17 AM

Originally Posted by DaveC426913

Gravity depends on one thing and one thing only: the mass.

Since you've replaced the sun with an equivalent mass - regardless of what that mass is - the gravitational force will not change.

Black holes do not have any more gravitational pull than any other object of an equivalent mass. What's unique about black holes is that you can get much closer to them, which is where gravity gets very strong.

Wow! Thank you!
I got it.

**Danger** · Nov4-09, 03:26 PM

Also, a 'normal' black hole created during a supernova event is much less massive than the original star. A huge part of the star is blown off as part of the explosion. Our sun is not massive enough for that to occur, though.