When astrophysicists were able to capture an image of a black hole for the first time in mid-April with the aid of the Event Horizon Telescope, it caused an even bigger sensation. Even though researchers were able to establish the effects of black holes (which proved their theoretical existence) much earlier, "seeing is believing" - as the old saying goes. And unlike the Higgs boson, black holes are a phenomenon with which most laypeople beyond the world of physics are familiar - not least due to science fiction books and films such as Interstellar.
Black holes have even found their way into everyday language - for instance, to symbolize something or somebody that has disappeared, never to be seen again. Our wallets and purses are good examples of black holes. The phenomenon also serves as an inspiration in music: The British rock band Muse named their fourth studio album Black Holes and Revelations; one of the strongest tracks on the record is "Supermassive Black Hole," which also appeared on the soundtrack of the vampire cliché trash film Twilig
Anyway, the first photo of a black hole made the headlines. Roughly speaking, it is an object whose mass is concentrated in an extremely small volume and generates a gravitational pull so immense that not even light can escape it. The outer edge of this area is the event horizon, within which nothing is able to escape the gravitational pull of the black hole.
There are various classes of black hole, which were formed in different ways. The simplest to understand are stellar black holes, which are formed when a star of a certain size collapses. The outer shells are shed into a supernova; the core collapses due to its gravitational pressure, forming an extremely compact body and becoming a dot-shaped object of infinitely high density - a singularity.
The supermassive black holes that lent their name to the Muse song can have a mass which is millions or even billions of times greater than that of our sun. Sagittarius A in the center of the Milky Way - our own galaxy - has a mass of 4.1 million suns, making it one of the supermassive black holes. The black hole photographed by the researchers also falls into this category, but is located in the center of the galaxy known as Messier 87.
In order to photograph it, scientists linked up a total of eight mega radio telescopes at six locations across four continents and on Hawaii and set them all to a frequency of 230 gigahertz to create a giant virtual telescope with a magnification factor of two million. A real telescope with the same power would be roughly the same size as the diameter of the earth.
The preliminary work for the photo of the black hole began two years earlier, with the first observations made in April 2017. The team of researchers observed the sky for five nights and recorded data for almost eight hours each night - 32 gigabits per second and a total of 3,500 terabytes of raw data. All of the data was stored on hard drives, one of which was flown to the Max Planck Institute for Radio Astronomy in Bonn and the other to the Massachusetts Institute of Technology in the USA. Here the researchers fed the data into their supercomputers. A total of four teams worked independently of another to develop images of the black hole based on this data. The photo is not an image made up of pixels, but a reconstruction of the waves received simultaneously by all of the radio telescopes.
The image not only proved the existence of black holes, but also confirmed Albert Einstein's general theory of relativity that made this observation possible in the first place. And like in the case of the Higgs boson, the fascinating thing about physics is that some theories can only be proved decades or even centuries later, once the technology is available. This makes the work of the spiritual fathers of these discoveries all the more impressive. Meanwhile, there is still no plausible theory as to what lies behind the phenomenon of the black hole in our wallet. Unfortunately.