It begins with "ds squared equals" ... yes, followed by 15 lower case letters, four capital letters, two Greek letters, four brackets, three fractional lines, nine superscript twos, three minus and one plus sign.

What for the sake of the universe does this mean? asks the shuddering layman. He is not alone. "Ever since mathematicians have been obsessed with the theory of relativity, I don't understand it myself," Albert Einstein is said to have said when other researchers began thinking about the consequences of his work more than 100 years ago. Einstein had discovered that the gravity of bodies can bend space and time. But how exactly? And how strong?

This was also the question asked by the German physicist Karl Schwarzschild (1873-1916), who shortly before his death presented this formula, which describes the gravitational field of a "mass point". It shows (albeit only mathematically at first): if large masses are concentrated in one point, a "singularity" is created. Strongly (!) simplified: A mathematical-physical boundary object, infinitely small, infinitely heavy, infinitely dense.

All physical laws cease to exist there; gravity becomes so great that even light cannot escape it (hence the name "black" hole). Such objects are giant cosmic hoovers, galactic monsters: an invisible boundary line, the "event horizon", is created in their vicinity. What crosses it never returns. Any direct observation with common scientific methods is impossible.

Einstein did not believe that this was possible. He was wrong. He was refuted by the British mathematician and physicist Roger Penrose. In a "remarkable work" in 1965, he "introduced new mathematical tools and proved with mathematical rigour that the formation of black holes is an inevitable consequence of general relativity", explains physicist Ulf Danielsson of the Nobel Committee. Penrose's work is still regarded today as "the most important contribution to general relativity since Einstein“.

What Penrose prepared mathematically, the two other researchers now honoured, the German Reinhard Genzel - who studied in Bonn and completed his doctorate at the Max Planck Institute for Radio Astronomy in Bonn - and the American Andrea Ghez, put into practice. Both led two independent research groups that have been investigating the centre of our Milky Way since the 1990s. Numerous stars there orbit around a common centre near the star "Sagittarius A*" - 26,000 light years away from Earth, the equivalent of 246 quadrillion kilometres.

Genzel, Ghez and their teams measured the orbits of these stars. Over the years and decades, they became more and more accurate, more and more precise. Until it was established that Sagittarius A* contains a "supermassive" black hole. Four million solar masses - eight million trillion quadrillion tonnes - are concentrated in what is cosmically the tiniest space (roughly the size of our solar system).

The bibliography of the Nobel "Explanatory" essay has 55 entries and reads like a prominent encyclopaedia of physics. Apart from Schwarzschild and Einstein, it also includes, for example, Stephen Hawking, the coordinator of atomic bomb inventions, Robert Oppenheimer, or the French mathematician and astronomer Pierre-Simon Marquis de Laplace (1749-1827): as early as 1799, he presented an essay according to which "the attractive force in a world body can be so great that the light from it cannot escape". Penrose is quoted with seven essays, Genzel with six, Ghez with three.

This shows how much such research is a collective human achievement. With all due respect for the work of Penrose, Genzel and Ghez; with all due respect for the highest of all research prizes: The fact that, according to the Nobel Statute, only a maximum of three researchers may receive the gold medal for such Olympic team victories is nonsense. Nothing works without preparation and preliminary work. One person always builds on the other.

More than 200 researchers from 20 nations and 59 institutions were involved when the first quasi "photographic" image of a black hole shook up the world a year ago, meticulously combined from data from the "Event Horizon" telescope. The object is called "M87" - after the galaxy "Messier 87", where it is located.

Radio telescopes work together like a single giant device of planetary dimensions

For the photo, eight telescopes on four continents were combined. They are located in Arizona, Hawaii, Chile, Spain and even Antarctica.

A special procedure coordinates them as if they were a single giant telescope of planetary dimensions. Each telescope provides gigantic amounts of data for such observations: For "M87" it was around 350 terabytes (14 000 Blu-ray discs) - every day.

This would never fit in an email: The data had to be transported on hard disks to the evaluation computers (including the Max Planck Institute for Radio Astronomy in Endenich). Not so easy when the telescope is in Antarctica.

The view into the unfathomable; the journey behind the event horizon, which began more than 200 years ago with Laplace, continued 100 years ago with Einstein and Schwarzschild and 55 years ago with Penrose even further: it does not end with the (price) prize announcement from Stockholm.

The work at the limits of human knowledge continues until it crosses all horizons. Andrea Ghez hopes that her and her colleagues' work will encourage young researchers - especially women - to continue along this path now. She says: "There is so much that can be done.

(Original text: Wolfgang Pichler / Translation: Mareike Graepel)