Why do things move away from the heat?

I was melting butter on the stove and I noticed that the butter moved away from the center of the pan on the eye.
so the middle of the eye, im guessing, is the hottest part of the eye.
why do things move away from heat?

It's probably:

1 - Dissolving much faster in the middle of the heat.
2 - Flowing down to the sides of the pan because the pan is slightly curved up in the middle.

A couple of reasons:
- Stuff expands when it melts (and expands further when it evaporates), so the melting butter is exerting outwards force on the remaining butter, pushing it away.
- Melted butter works as a lubricant to make it easy for the remaining butter to slide off.

Gravity probably had more to do with it - the center of the pan may be naturally cupped upwards, or expanded that way from the heat. Then the liquefied butter acted as a lubricant allowing the hard butter to flow to the lower part of the pan.