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How and why black holes rotate

How and why black holes rotate

Black holes are often illustrated in the non-rotating canister, as they are easier to explain. But in reality they take turns.

The current best theory of gravity, general relativity, published by Albert Einstein in 1916, predicts the existence of so-called spinning black holes, which we actually observe. Not only. The same theory distinguishes between electrically charged and discharged, but hereafter we shall confine ourselves to the study of the latter case only. So let’s see How and why black holes downloads take turns.

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What is the difference between rotating and non-rotating black holes?

Artist’s impression of a spinning supermassive black hole surrounded by an accretion disk. Credits: ESA/Hubble, ESO, M. Kornmesser.

He must first remember the concept of angular momentum. Whatever the formal and more general definition of the moment, you will have already learned in school that angular momentum is a quantity that characterizes the rotation of an object in some way: for example, with respect to a given reference system, a fixed top has angular momentum sum null; However, when in rotation, this quantity becomes non-zero. In particular, when no external forces are able to change the rotational state of the top, the total angular momentum is conserved.

Let’s go back to black holes and consider the most common of them, that is, those that were formed as a result of the gravitational collapse of a star. It is likely that the latter turned around before collapsing. Just like the spinning top, we can assume that the star also has non-zero angular momentum. Assuming that it was isolated during collapse, that would mean that angular momentum must be conserved: thus the formed black hole has the same angular momentum as the star before it collapsed. However, in this context, this does not mean that the black hole is spinning in the classical sense of the term, like a star or a top. In fact, this rotation manifests itself in ways that are not at all familiar to us.

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First, unlike the non-periodic case, the singularity (a region of infinite density where all matter is concentrated) of a spinning depletion black hole is a ring, not a point. This singularity can also be surrounded by up to two event horizons (a boundary from which nothing can exit), rather than just one. Moreover, near such a black hole, the body will be “pulled” to rotate around it. Then the whole is surrounded by the so-called ergosphere, that is, a region in which, in order to resist the aforementioned pull, it is necessary to exceed the speed of light in a vacuum (which is impossible). In short, you now have another reason to get away from black holes.

source: Princeton University Press.

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