To understand the distinction between rotating and non-rotating black holes, we must first grasp the concept of angular momentum. For simplicity, think of a spinning top. When stationary, the top possesses zero total angular momentum. However, once it spins, this value becomes non-zero. If there are no external forces to alter the state of the spinning top, the total angular momentum remains constant.
Applying this concept to black holes, specifically those created through the gravitational collapse of a star, we can infer that the star, prior to its collapse, was likely rotating and therefore held a non-zero angular momentum. If the star was isolated during its collapse, the angular momentum would remain constant, resulting in the black hole having the same angular momentum as the pre-collapsed star. However, this does not mean the black hole rotates in the traditional sense, like a star or a spinning top. Its rotation manifests in unfamiliar ways.
First, a rotating, discharged black hole's singularity (a region of infinite density where all matter is concentrated) presents as a ring, unlike the point-like singularity in non-rotating cases. This singularity can be encompassed by up to two event horizons (the point of no return from which nothing can escape), as opposed to just one. Additionally, near such a black hole, an object would seem to be 'dragged' into rotation around it. All of this occurs within the ergosphere, an area where, to counteract the aforementioned dragging effect, one would need to exceed the speed of light in a vacuum, an impossibility. Therefore, it's advisable to maintain a safe distance from black holes.
Source: Princeton University Press.
Post a Comment