Into the Heart of Darkness
For a long time, black holes were something that could only be made comprehensible with formulas. Now astrophysicists have photographed one of the mass monsters with telescopes. A picture for the history books - and the current highlight of a long journey.
In the end the weather is as merciful as it has been for years. Everywhere the view is clear: in the Martian wasteland of the Chilean Andes, on top of an extinct volcano in Mexico, on an overgrown ridge in Arizona, in Spain's Sierra Nevada, on Mauna Kea in Hawaii and at the South Pole. At first the scientists hesitate, then one of them gives the start signal - and at each of the locations, telescope dishes as high as a house swing into position.
One of their goals on this April day in 2017: an insanely small speck in the constellation Sagittarius. Astronomers have long suspected that there, at the center of our galaxy 26,000 light-years away, is a black hole called Sagittarius A. It is estimated that it is 4.3 million times the mass of our sun. It is the place around which the Milky Way's spiraling arms revolve. At the same time, it is a symbol of the limits of our civilization's knowledge: humans have never seen a black hole. So far they have only been able to infer the existence of the bizarre objects indirectly.
The parabolic antennas distributed around the globe keep an eye on the region for hours. Again and again they peek into the center of another galaxy called M87, which is located in the night sky in the constellation Virgo and in whose heart an even more massive black hole is said to be hiding.
The observation by the telescope network, which the scientists have christened the Event Horizon Telescope (EHT), lasts five days. The eight observatories record 3,300 terabytes of data during this time – far too much to transmit over the Internet. So the researchers pack around 1,000 hard drives in padded boxes and have them flown to Boston and Bonn for evaluation.
Two years later, on April 10, 2019, there is finally a result: the international team of around 200 scientists presented a recording of the EHT at no fewer than six press conferences. It only shows a faded red ring against a dark background. But the researchers are certain: Here you can see the black hole in the center of the distant galaxy M87 - or rather its outline…
