Do black holes rotate like planets?

Black holes are very special objects in the universe. A black hole is born from the collapse of a very large mass into a point of extremely high density.

It creates an infinitely curved region of space-time, from which nothing can escape, not even light. Do black holes rotate? This is an interesting but not so simple question that I received in one of my recent lectures. To answer it completely and accurately, we need a clear understanding of the very verifiable properties of black holes as well as about the nature of rotation. To date, the concept of rotating black holes is not new. In fact, every object in the universe, once having a mass large enough to be spherical, will also have a rotation. Since mass exerts gravity, every object tends to compress itself – because its parts attract each other. For small masses, this gravitational compressive force – commonly known as centripetal gravity – is so small that it cannot exert any effect on the object, because it is simply an intermolecular force of cohesion. substance – especially solids – is much larger than it is. But with very large masses, on the other hand, the force of gravity is so great that matter will rearrange until it becomes spherical. That is, the state in which the force of gravity directed at the center of the object from all directions is equal to each other. That’s how every object as large as a planet or a star gets its spherical shape. At the same time, when there is such a large mass, another problem arises, and also related to gravity. Since no single star or planet is perfectly uniform, in fact the gravitational forces in their different regions are unequal. This difference is the main reason they oscillate, and hence the rotation. Thus, all large objects in the universe rotate because of their own gravity. What about black holes? The most common types of black holes known to scientists today are stellar-mass black holes. It is formed from the late-life contraction of the cores of massive stars. These stars are usually at least 8 to 10 times the mass of the Sun. Towards the end of their lives, their cores shrink very rapidly because the fusion reaction no longer produces enough energy to resist the contraction of that enormous mass. This sudden contraction causes an explosion that is considered one of the most violent events in the universe” supernova explosion. This explosion tore apart the stellar shell that was previously in the state of a red supergiant. The remaining core of the star shrinks and collapses to become a black hole. All stars rotate on their own axis (our Sun, for example, has a rotation period of more than 25 days). It is not difficult to speculate that something formed from a rotating stellar core would also have to rotate, because that momentum is simply still there. The same is probably true of supermassive black holes – black holes with masses ranging from hundreds of thousands to billions of times the Sun, located at the center of most galaxies ever observed. In fact, when the first image of a black hole was released in 2019, scientists were able to see the spirals of the accretion disk surrounding the black hole. It shows that the giant accretion disk is rotating, not fixed. Just like the fact that all the stars in each galaxy are constantly moving around the center of the galaxy (for example, our Sun takes about 230 million years to complete one full circle around the center of the Milky Way). Two things need to be clarified before concluding that the black hole rotates on its own The entire initial mass of the black hole – in theory – is packed into an extremely small singularity. It is so small that it can mathematically be considered sizeless. That singularity has a certain radius (Schwarzchild radius) known as the black hole’s event horizon, but it is just a region of pure space-time, not an object like it has a surface. like a star or a planet. As such, it is difficult to consider something with no dimensions, or a boundary without a surface, to be rotating, since there is simply no alternate motion of points to a particular surface. No radiation comes out from within the event horizon, which also means that all information inside a black hole is unknown. If matter were indeed crushed and completely collapsed into a single point, the space within the event horizon could itself be a place of absolute uniformity, i.e. no rotation would occur due to the difference. interesting. With these two points in mind, don’t forget that what we see spinning is itself just the accretion disk surrounding the black hole. Of course, one can also calculate the rotational speed of an accretion disk based on its mass when taking into account as well as when not taking into account the presence of a black hole at the center, from which to compare and predict. It looks like the black holes in those places are spinning very fast. Even so, given that we don’t know anything about what lies within the event horizon, or even something specific happening at its very edge, concluding that black holes are indeed rotate or not and how fast they rotate is still too early. Likewise, the charge of a black hole is also a purely theoretical concept and is calculated from solving Einstein’s equations. There is no way for us to verify if an electric charge really exists after being swept inside the black hole’s event horizon. In the future, to know more about this information, we will need to look forward to new generations of telescopes and new methods to image and track more black holes with much greater detail. compared to what there are today.