A supermassive body of four million solar masses has been discovered near the center of our Galaxy. True, it is invisible, inaudible and intangible.
Finger to the sky?
A group of German physicists from the Max Planck Institute for Extraterrestrial Physics recently made a sensational statement: they obtained evidence that there is a black hole in our Galaxy.
- For about twenty years, we have been observing the movement of several dozen stars near the center of the Galaxy, located at a distance of 27 thousand light years from the Sun, says the head of the group, Reinhard Hansel. - The orbits of these stars indicate that the concentration of mass located in the center is, without a doubt, a black hole.
Does this threaten our Galaxy? Will the space monster eat the Earth?
It turned out that so far there are no answers to these questions. According to the director of the State Astronomical Institute. PK Sternberg Moscow State University Corresponding Member of the Russian Academy of Sciences Anatoly Cherepashchuk, observing the orbits, a black hole cannot be calculated.
- To prove that the body located in the center of our Galaxy is a black hole, you need to do two things, - the scientist explained to reporters. -First, experimentally show that the radius of this body is equal to the so-called gravitational radius for a black hole of a given mass (and for a black body of four million solar masses, it is equal to about seven solar radii). And, secondly, to prove that this body does not have a solid surface, but instead an event horizon.
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According to Cherepashchuk, both of these tasks are in principle feasible, and in 20 years, he hopes, scientists will be able to say for sure whether it is a black hole or not.
In general, the question: to be or not to be our Galaxy is postponed for two decades. In the meantime, let's get to know this monster better.
The most wicked place
There is no more mysterious and frightening object in space than a black hole. One phrase already inspires unaccountable fear: it paints the image of an all-consuming abyss. Before her, not only ordinary people are in awe, but astrophysicists are also in awe. “Of all the creations of the human mind, from mythological unicorns and dragons to the hydrogen bomb, perhaps the most fantastic is the black hole. A hole in space with very specific edges, into which anything can fall and from which nothing can get out. A hole in which the gravitational force is so great that even light is captured and held in this trap. A hole that bends space and distorts the flow of time. Like unicorns and dragons, black holes seem to be attributes of science fiction or ancient myths rather than real objects. However, the existence of black holes inevitably follows from physical laws. There may be millions of them in our Galaxy alone,”said Kip Stephen Thorn, a well-known scientist, head of the department at the California Institute of Technology (USA), member of the US National Academy of Sciences, member of the NASA Scientific Council, about black holes.
In addition to their fantastic power, black holes have an amazing ability to change space and time within themselves. They first twist into a kind of funnel, and then, having crossed a certain border in the depth of the hole, they decay into quanta. Inside the black hole, beyond the edge of this peculiar gravitational abyss, from where there is no exit, amazing physical processes are flowing, new laws of nature are manifested.
According to many experts, black holes are the greatest sources of energy in the universe. We probably see them in distant quasars, in exploding galactic nuclei. It is assumed that black holes in the future will become sources of energy for humanity.
The end of the world is here
How do black holes form? According to astrophysicists, most of them arise after the death of large stars. If the mass of a star is twice that of the Sun, then by the end of its life the star can explode as a supernova. But if the mass of the substance left after the explosion still exceeds two solar mass, then the star should collapse into a tiny dense body, since gravitational forces completely suppress any internal resistance to compression. Scientists believe that it is at this moment that a catastrophic gravitational collapse leads to the emergence of a black hole. They believe that with the end of thermonuclear reactions, the star can no longer be in a stable state. Then for a massive star there is only one inevitable path - the path of universal and complete contraction, turning it into an invisible black hole.
Why are they invisible?
- The very name "black holes" suggests that this is a class of objects that cannot be seen, - explains the head of the radio astronomy department of the State Astronomical Institute named after Sternberg, Candidate of Physical and Mathematical Sciences Valentin Esipov. - Their gravitational field is so strong that if somehow it were possible to get near the black hole and direct the beam of the most powerful searchlight away from its surface, then this searchlight could not be seen even from a distance not exceeding the distance from the Earth to the Sun.
Indeed, even if we could concentrate all the light of the Sun in this powerful searchlight, we would not see it, since the light would not be able to overcome the influence of the gravitational field of the black hole on it and leave its surface. That is why such a surface is called the absolute event horizon. It represents the border of a black hole. And what is hiding there, abroad?
Let's walk to Hell
The most interesting description of the "interior" of a black hole belongs to the already mentioned American physicist and astronomer Kip Stephen Thorne. “Imagine yourself as the captain of a large star-class spacecraft. -proposes the scientist in his book "Travel among black holes". - On the instructions of the Geographical Society, you have to investigate several black holes located at great distances from each other in interstellar space, and transmit a description of your observations to Earth using radio signals.
Having been on the way for 4 years and 8 months, your ship slows down in the vicinity of the closest black hole to Earth, called Hades (Hell) and located near the star Vega. The presence of a black hole is noticeable on the TV screen: hydrogen atoms scattered in interstellar space are pulled inward by its gravitational field. Everywhere you can see them moving, slow away from the hole and faster and faster as you get closer to it. This is similar to the fall of water in Niagara Falls, except that atoms are falling not only from the east, but also from the west, north, south, from above and from below - from everywhere. If you don't do anything, you too will be pulled inward.
So, with the greatest care you have to transfer the spaceship from the trajectory of free fall to a circular orbit around the black hole (similar to the orbits of artificial satellites orbiting the Earth) so that the centrifugal force of your orbital motion compensates for the gravity of the black hole. Feeling safe, you turn on the ship's engines and prepare to study the black hole.
First of all, through telescopes, you observe electromagnetic radiation emitted by falling hydrogen atoms. Far from the black hole, they are so cold that they only emit radio waves. But closer to the hole, where the atoms fall faster, they collide from time to time, heat up to several thousand degrees and start emitting light. Even closer to the black hole, moving much faster, they heat up due to collisions to several million degrees and emit X-rays.
As you point your telescopes "inward" and continue to approach the black hole, you will "see" gamma rays emitted by hydrogen atoms heated to even higher temperatures. Finally, in the very center, you will find the dark disc of the black hole itself.
Your next step is to carefully measure the length of the ship's orbit. This is approximately 1 million km, or half the length of the Moon's orbit around the Earth. Then you look at the distant stars and see them moving like you. Observing their apparent movement, you find out that you need 5 minutes. 46 s to make one revolution around the black hole. This is your "orbital period".
Knowing the period of revolution and the length of its orbit, you can calculate the mass of the black hole Hades (Hell). It will be 10 times more sunny. This is, in fact, the total mass accumulated in the black hole throughout its history and includes the mass of the star, as a result of the collapse of which about 2 billion years ago the black hole was formed, the mass of all interstellar hydrogen drawn into it since its birth, and also the mass of all asteroids and lost starships that fell on it.
The most interesting are the properties of its surface, or horizon - the boundary, because of which everything that falls into the hole can no longer return. Borders that will prevent a spaceship and even any kind of radiation from getting out: radio waves, light, X-rays or gamma rays …
Although you can calculate all its properties from the outside from the mass and angular momentum of a black hole, you cannot know anything about its interior. It can have a disordered structure and be highly asymmetric. All of this will depend on the details of the collapse that formed the black hole, as well as on the features of the subsequent pulling in of interstellar hydrogen, so the diameter of the hole simply cannot be calculated.
With these results, you can explore the vicinity of the black hole horizon …
Saying goodbye to the team, you climb into the descent vehicle and leave the ship, remaining at first in the same circular orbit, continues the physicist Thorn. - Then, by turning on the rocket motor, brake slightly to slow down your orbital motion. In this case, you begin to spiral closer to the horizon, moving from one circular orbit to another. Your goal is to enter a circular orbit with a perimeter slightly longer than the horizon. As you move in a spiral, the length of your orbit gradually decreases - from 1 million km to 500 thousand, then to 100 thousand, 90 thousand, 80 thousand. And then something strange begins to happen.
Being in a state of weightlessness, you are suspended in your apparatus, let's say, with your feet - to a black hole, and your head - to the orbit of your ship and the stars. But gradually you begin to feel that someone is pulling your legs up and down - by the head. You realize that the reason is the attraction of the black hole: the legs are closer to the hole than the head, so they are attracted more strongly. The same is true, of course, on Earth, but the difference in the attraction of the legs and the head there is negligible, so no one notices it. Moving in an orbit 80 thousand km long above the black hole, you feel this difference quite clearly - the difference in attraction will be 1/8 of the Earth's gravity (1/8 g). The centrifugal force generated by your movement in orbit compensates for the attraction of the hole at the center point of your body, allowing you to float freely in zero gravity.but your legs will be affected by an excess of 1/16 g, while the head, on the contrary, will attract weakly, and the centrifugal force will pull it up with exactly the same additional acceleration of -1/16 g.
Somewhat puzzled, you continue along the spiraling spiral, but surprise quickly gives way to concern: as the size of the orbit decreases, the forces stretching you will increase more and more rapidly. With an orbital length of 64 thousand km, the difference will be 1/4 g, with 51 thousand km -1/2 g and with 40 thousand km it will reach the full earth's weight. Gritting your teeth from exertion, you continue to move in a spiral. With an orbital length of 25 thousand km, the tensile force will be 4 d, i.e. four times your weight in terrestrial conditions, and at 16 thousand km -16 g. You can no longer stand upright. You are trying to solve this problem by curling up into a ball and pulling your legs up to your head, thereby reducing the difference in power. But they are already so large that they will not allow you to bend - they will again be extended vertically (along the direction radial with respect to the black hole).
No matter what you do, nothing will help. And if the spiral movement continues, your body will not stand it - it will be torn apart. So, there is no hope of reaching the vicinity of the horizon …
Overwhelmed, overcoming the monstrous pain, you stop your descent and transfer the device first to a circular orbit, and then carefully and slowly begin to move along an expanding spiral, switching to larger circular orbits until you reach the starship."
Thorne's story sounds like a fantasy so far. And it is calculated for the time when a person will achieve such success in the development of technology and technology that intergalactic flights and the construction of ring worlds around black holes will become a reality. And according to the most optimistic forecasts of futurologists, this will become possible no earlier than in 50 years.
No guys, it's not like that …
It must be admitted that many scientists still deny the existence of black holes. After all, their discovery and study takes place at the tip of the pen. And recently, an even more unexpected assumption has appeared that black holes are not holes at all, but some objects, more akin in nature to Bose-Einstein condensate bubbles (the state of aggregation of matter, the basis of which is bosons, cooled to temperatures close to absolute zero). This new hypothesis was put forward by researcher Emil Mottola of the Theoretical Branch of Los Alamos National Laboratory, along with co-author Pavel Mazur of the University of South Carolina in the United States.
The researchers' explanation introduces a radically new look at the nature of black holes, which are not presented as "holes" in space, where matter and light inexplicably disappear in the event horizon zone, but rather as spherical voids surrounded by a special form of matter never before known on Earth. Mazur and Mottola call these objects not black holes, but gravitational stars.
Inside a gravitational star, space and time are reversed, as in the black hole model.
Mottola and Mazur even suggest that the universe we live in may be the inner shell of a giant gravitational star.
S. Kuzmina. "Russian space"
