Celestia Forums

Hi.
One day I started thinking "What happens if two objects of the same mass are placed near each other?" I figured they would orbit around each other similarly to Charon and Pluto. Am I right? If I'm not, what would happen?

In order for them to "orbit" they must both have angular motion, in a direction that is not on a collision course with each other. If you start them at 100% static state, then both object will head directly towards each other and collide.

So basically as long as they're moving fast enough and in certain directions, they'll move around each other and won't collide, but if they're not, they'll eventually head for each other and collide?

The angular motion MKruer is refering to should be considered as the relative motion of both objects perpendicular to the direction of the gravitational force between the objects at the moment you set your simulation in motion. If this speed it just right you get a stable system in which both objects orbit a common barycentre. If their masses are identical, this barycentre will be halfway both objects. In the case of - for instance - the earth and the moon the barycentre is closer to the heavier object (earth) and actually it is inside earth.

Once you have found the right value for your simulation there will be little disturbance over time if your system is limited to just these two bodies. Remember, there is little to no friction.

Oh, now I get it! Thanks.

another interesting observation:

If they rotate at the beginning relative to each other, depending on the masses and the distance, they begin to lock their rotation (around the individual axis) with the revolution around each other, so only one side is visible form each other. this is due to tidal friction. This happened for example with teh Moon