The white ball is the “DefaultSceneRoot” component. It essentially represents the origin of the actor’s transformation, rotation and scale values.
You cannot get rid of it but it can be replaced by a different component which you would like to be the root component instead. If this has no visual aspect you will not see it in the viewport. Keep in mind this new root will be unable to be moved or rotated!
Edit: Just saw Jacky’s answer, that one is definitely better as you won’t be messing around with the root component in an irreversible way.