The dark mystery of the Milky Way: black holes have been officially recognized

For half a century black holes have gone from “a hypothetical object, not prohibited by the general theory of relativity” to the fundamental part of the universe, the reality of which is no one else is disputed. The Nobel Prize in Physics in 2020 is a recognition of the enormous work of astrophysicists and cosmologists who have investigated in the smallest detail what seems to be impossible to even observe.

Not all sensational scientific discoveries are announced on the front pages of newspapers. Some striking scientific facts come into our lives on the contrary: what has recently been a bold hypothesis, a decade later becomes a universally recognized reality, but when and by whom the discovery was made, humanity will know only after time. Approximately it happened with black holes.

In popular science books of the middle of the last century about black holes it was accepted to write that this is a hypothetical object, the existence of which follows from Einstein’s General Theory of Relativity, but to prove the reality of such objects is extremely difficult, if at all possible. In 2017, the Nobel Prize was awarded for the registration of gravity waves emitted in the collision of black holes, and soon received a photograph of a black hole. However, for half a century, no one has not bothered to tell humanity that the opening of black holes took place, and it is no longer a hypothesis but reality.

Perhaps this moment has come now, when in Stockholm announced the names of winners of the Nobel Prize in Physics in 2020. It was awarded for the theoretical justification of the existence of black holes, as well as for the opening of a black hole in the center of our galaxy Milky Way.

Half of the prize will be awarded to Roger Penrose, British physicist and mathematician and head of the Mathematics Department at Oxford. He was awarded the award for proving that the formation of a black hole is a direct consequence of the general theory of relativity. The remainder will be shared by Reinhard Genzel from Germany and Andrea Gez from the United States for the discovery of a supermassive compact object in the center of our galaxy. Genzel and Gez showed that this object is a black hole.

Black holes are objects with the most powerful gravity in the Universe. Even light cannot break out of the black hole. In a black hole, space is collapsed into a singularity and time stops. The possibility of such objects follows from Albert Einstein’s General Theory of Relativity (GTO). To date, this theory has been tested many times and very carefully in a variety of ways, from astronomical observations to experiments with chronometers.

The OTO equations are extremely difficult to solve in general. As for black holes, it has long been known that their existence is not prohibited by UTO. However, one thing is one thing – an object that is “not prohibited by the theory”, but it is not clear how and under what conditions it can form, and quite another thing – something that naturally follows from the theory and simply cannot not exist in reality. This is exactly the step that Roger Penrose made in the theory of black holes. In 1965 he published a paper showing how in many cases the most important properties of space-time can be found out without precise solutions. With these methods Penrose has received the most important result: he proved that black holes are formed naturally after the explosion of the most massive stars (weighing dozens of suns).

This article by Penrose is still considered to be the most important publication on UTO since Einstein’s work. It should be noted that an important contribution to these studies was made by Stephen Hawking, one of the fundamental theorems related to the problem of black holes, called the Hawking-Penrose theorem.

To date, the formation of black holes as a result of a supernova explosion, discovered by Penrose at the tip of the pen is a universally recognized fact. However, for discoveries “at the tip of the pen”, as is known, Nobel prizes do not give: the result obtained theoretically must be confirmed by observation or experiment. Where can one observe these mysterious black holes? It turned out that one of them is very close to us. Our very galaxy, which we see from Earth as a smoky plume of the Milky Way plus a scatter of nearby stars, is spiralled around a supermassive black hole. The decisive proof of this fact was obtained by Reinhard Genzel and Andrea Gez.

Each of these two laureates led his own team to study the object Sagittarius A*. This compact body is located in the heart of the Galaxy. Sagittarius A* is a powerful source of radiation in a variety of ranges, from radio waves to X-rays.

To find out its nature, astronomers have sought to determine its mass and size. To do this, they observed stars turning around this body.

Genzel and Gez had to develop special methods to observe these luminaries even through the thicknesses of gas and dust covering the center of the Galaxy. As a result of many years of work, the laureates and their employees mapped the orbits of the stars circulating around Sagittarius A*.

It turned out that this object has a mass of four million solar masses, but it is comparable in size to the solar system. An object of such enormous density cannot be anything but a black hole. Thus, Genzel and Gez not only found out the nature of Sagittarius A*, but also received the first undeniable observation evidence of the existence of black holes.

Today, it is generally accepted that Sagittarius A* is a supermassive black hole, which falls on its surrounding substance. This matter also emits radiation that turns a black hole into a very bright object.