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.

The idea behind the study of nuclear fusion is to recreate how the Sun generates enormous amounts of energy, a process involving a large amount of heat and pressure that combine to form plasma, in which atomic particles fuse. with super speed. Scientists are looking to trigger and study these reactions on Earth with a variety of experimental equipment, but experts say that EAST, located at the Hefei Institute of Physical Sciences of the Academy of Sciences Chinese studies, is the most promising approach. Inside China’s “Artificial Sun”, the Tokamak Superconducting Reactor (EAST). Photo: Newatlas. The EAST is a metal toroidal device consisting of magnetic coils designed to sustain streams of superheated hydrogen plasma long enough for the above reactions to occur. In 2016, scientists at EAST heated a hydrogen plasma to about 50 million degrees Celsius and maintained it for 102 seconds. Then in 2018, they hit 100 million degrees Celsius, six times hotter than the Sun’s core, and lasted 10 seconds. According to the Xinhua , the latest test marks a big step forward, achieving a new record when heating the plasma to 120 million degrees Celsius and maintaining it for 101 seconds. In separate experiments, this “artificial sun” heated plasma to 160 million degrees Celsius in 20 seconds. The goal of EAST is to maintain the plasma at 100 million degrees Celsius for more than 1,000 seconds (about 17 minutes). These experiments are not designed to generate conventional electricity, but to advance the field of synthetic physics for next-generation devices such as ITER, the world’s largest nuclear fusion reactor is expected to be. completed by 2025. Similar to EAST, experiments on South Korea’s KSTAR reactor set a world record last year, maintaining plasma at more than 100 million degrees Celsius for 20 seconds. In addition, the country also announced the development of ITER and is expected to officially operate in 2035.

Exploring the stars is man’s way to the universe. Some people think that each star represents a destiny, others say that the stars are small angels tasked with lighting up the night. Today, science has been able to give us a more precise answer. What is a star? Stars are all celestial bodies that are capable of emitting their own light. All of them are giant air spheres. They are tens to hundreds of thousands of times more massive than Earth. Only thanks to such a large mass can they create their own light. An object to be able to emit its own light needs to have a mass of at least 70 times the mass of Jupiter – the largest planet in the Solar System, that is, about 7% of the mass of the Sun. Why do we see the stars? The stars in the sky have always been a mystery to the human imagination. Our Earth has a mass of about 6x1024kg (6 million billion billion tons). The Sun is 330,000 times heavier than the Earth. That is, a star with a mass of 7% of the mass of the Sun would be about 23,000 times heavier than the Earth. Every object has a gravitational force that directs the center of it to its heart. Normally no one notices but we ourselves are always attracted to our own. Because each part of the body is attracted to each other and the sum of them all form a gravitational force directed towards a center of mass in our body (the center of gravity of the object). The table, the chair, the Earth, are always gravitating to itself by a force called centripetal gravity. But why doesn’t it all burn brightly? That’s because the mass of the objects we come into contact with every day just can’t afford that. Because gravity is a force proportional to mass, gravity in everyday objects is so small that they don’t cause any significant effects. With very large objects such as planets, Earth, gravity is also negligible because it creates a clear attraction that pulls everything towards it. For example, when you jump high, you will fall very quickly because of the pull from the Earth. As for the aforementioned massive objects (tens of thousands of times heavier than the Earth), the great gravity makes the pressure at the center of the celestial body very high, this pressure provides a great acceleration for the celestial bodies. gaseous atoms (mostly hydrogen). They collide strongly with each other at high velocities, breaking the electron shells, separating electrons from the atomic nucleus. At the core of the star is no longer ordinary gas but a state of chaotically moving nuclei and electrons. This state is called plasma. In the plasma state, the hydrogen nuclei have a chance to collide directly with each other at high velocities, which causes what we call fusion reactions, fusing hydrogen nuclei into heavy hydrogen and finally is the helium nucleus. This reaction is known on Earth in hydrogen bombs – bombs capable of releasing thousands of times more energy than atomic bombs of the same mass. The fusion reaction at the core of a star releases a lot of energy in the form of radiation, some of which is visible light. This radiation is transferred to the star’s surface and causes the star to glow. Stars are composed mainly of hydrogen (over 70%), with a large part helium remaining, and an insignificant fraction of heavier gases. The surface temperature of a star is usually in the range of 3,000 to 50,000K, and the temperature at the center is in the range of several million to several tens of millions of K. It can be as high as 100 million K for red giants and several billion K. with red supergiant stars. Star classification Graphic image. By mass, stars are divided into two types, dwarfs and giants. Today, modern division is based on spectral charts. In which, the star with the obtained spectrum of which position on the chart will be determined to belong to which group with specific characteristics of mass and temperature. The most widely used spectrogram today is the Hertzsprung-Russell chart. This graph represents the luminosity, size, and temperature of any star when its spectrum is obtained. According to temperature, the chart is divided into 7 levels with the symbols O, B, A, F, G, K, M respectively. In which, the star closer to O is hotter and closer to M is cold. Each level itself is divided into several sub-levels. Through the chart, it can be seen that most of the stars in the universe are concentrated in the main sequence of the chart. This sequence is a sequence of dwarfs and subgiant stars. Our sun is also on this sequence. It is located in the G group, has the detailed spectral designation G2V (yellow dwarf/Yellow dwarf). Below the sequence are groups of white dwarfs, and above are giants and supergiant, supergiant stars. Star evolution All stars form from large clouds of dust and gas called protostar nebulae. Due to gravity they gather together and shrink until they form a dense mass. As we all know, all objects that carry mass carry gravity. The same object itself also has a force of attraction between different parts of it. However, the gravitational force between small masses is negligible and we hardly notice it. Only significant forces, such as Earth’s gravity acting on people and objects, are enough to be noticed. In stars, gravity is very strong (due to its high mass). When the force of gravity is too great for the atoms to bear, they break the atomic shells and accelerate their nuclei. Hydrogen nuclei (consisting of 1 proton) when collided at high velocity, combine to form heavy hydrogen, and then helium. This reaction releases energy that causes the star to burn brightly. This is a fusion reaction (also known as a nuclear explosion. This reaction is used in the hydrogen bomb (H bomb) – the most destructive destructive weapon that mankind has built). Thanks to the great energy released from nuclear fusion in the star’s core, the gravitational contraction is halted as the released energy balances the gravitational force. The star burns so brightly for several tens, hundreds of millions or billions of years. The lower the mass of the stars, the longer the lifespan. For example, our Sun is a dwarf, medium mass, it can live for about 10 billion years. Meanwhile, stars are much larger, sometimes only living a few hundred or even tens of millions of years because the high mass creates greater pressure towards the center. It causes nuclear fusion to happen faster and the star to deplete energy faster. After burning out all of its hydrogen energy, the star no longer produces energy against centripetal gravity. It will once again shrink. At this time, the helium nuclei combine to form nuclei of heavier elements such as carbon, oxygen and heavier elements up to iron. This process releases an energy that inflates the star’s crust while the star’s core continues to contract. This is the red giant stage. For medium-sized stars (with a mass between 0.5 and 10 times the mass of the Sun), the red giant shell, when inflated sufficiently large, will explode and break up to form a planetary nebula. Meanwhile, high-mass stars have massively inflated stellar shells, becoming red supergiant stars. During this stage, the stellar core continues to contract due to gravity, temperature and pressure both increase many times compared to the previous stage, allowing nuclei of heavier elements to be synthesized (from familiar metals). from copper, silver, and gold to radioactive elements). Up to a certain limit, the energy released from the core creates a large explosion that breaks the outer shell. This is a supervova explosion. After the shell is broken, the star’s core remains for both massive stars as well as light stars. For low- and medium-mass stars like the Sun, the core will stop shrinking, becoming a white dwarf, emitting a very faint light. After billions or tens of billions of years, the generation of radiation ends, stars no longer emit light. It’s called a black dwarf, a dark, dead mass of matter. In fact, the process for a white dwarf to become a black dwarf is so long that so far a black dwarf is only a theoretical prediction. No white dwarf in the universe has been around long enough to become a black dwarf. For massive stars whose core remains after the supervova are at least 1.4 times more massive than the Sun, the mass is so great that they continue to shrink. The nuclei react with each other to form heavy nuclei. The contractions are not over yet, they cause the free electrons to be squeezed tightly against the protons, combining to form neutrons. The star becomes a solid mass of matter, composed entirely of neutrons. Therefore, it has extremely high density and extremely fast rotation speed. This object is called a neutron star. Previously, when this object was first observed, astronomers saw that it emitted a very strong amount of electromagnetic pulses, so they called them pulsars. Even more massive stars with a core mass at least 2 or 3 times that of the Sun, have not stopped after reaching the neutron star stage. They squeeze all matter together to an infinitely large density, concentrated at a location called a singularity. This singularity warps the space around it, a region of space that is bent to an infinite (closed) curvature. The boundary of this space is called the event horizon. Because the space is bent inward, anything that goes in can’t get out, not even light. This entire region of space bounded by the event horizon is called a black hole.