A “breakthrough for humanity”: 200 astrophysicists in a telescope network were able to capture the first image of a black hole. This confirms Einstein’s general theory of relativity.
The layman does not see much: a dark spot, surrounded by a glowing ring. But rarely was a recording expected with such tension as this. At six concurrent press conferences around the world, the team from the event Horizon telescope network announced a “tremendous breakthrough for humanity” on Wednesday afternoon: the first shot of a black hole. The picture not only provides new insights into these most extreme phenomena of the universe. Above all, it impressively confirms one of the most important cornerstones of our physical view of the world: the general theory of relativity that Albert Einstein set up over a hundred years ago. Here are the backgrounds of this memorable “Astro-Show”.
Not the hole itself. It’s about a place where mass is extremely compacted. Gravity not only captures matter but also light and other electromagnetic radiation. In the gullet of a black hole, the information disappears forever. Within the “event horizon” that limits it, space-time events can no longer be observed. In the innermost point, the “singularity”, then even the laws of physics are suspended.
But the influence on the environment is very visible. If the black hole does not “eat” matter and rays that expand its mass, there is nothing to see just outside of it; its existence can then be proved, for example, by the effect of gravity on the orbit and speed of other celestial bodies. But when matter does fall, it is accelerated close to the horizon of events and becomes hot by the friction of a few million degrees. The energy released makes them shine brightly.
So, as a visible silhouette of the invisible black hole, you expected a glowing ring – and that expectation was not disappointed.
Roughly speaking, there are two groups of these phantoms of the universe: less severe ones that are created when a star burns out – leaving a supernova explosion to collapse into the black hole. And “supermassive” located in the center of a galaxy (presumably by everyone, maybe stabilizing them too). How they came about is still a mystery. Two such mass monsters were in the sights of the project. The researchers found what they were looking for in the giant galaxy Messier 87 (or M87 for short), one of the Milky Way’s largest neighbors in the constellation of the Jungfrau. At its center is a black hole that has 6.5 billion times more mass than our sun. Its event horizon has a diameter of 40 billion kilometers, which is more than three times the orbit of Pluto. You can not see that in the small black spot on the picture. The object is also 55 million light-years away. The images also show that the glowing ring is spinning, almost at the speed of light. That’s what we’re dealing with the rotating black hole. It’s not only bending space-time but also lets it spin with it. The matter does not fall directly into it but rotates on a rotating disk. Partly it is pulled into the hole as water flows in a whirlpool into the drain of a washbasin. In part, however, it is also thrown out into space. It not only bends space-time but also lets it spin with it.
Unable to succeed is a picture of the second, much closer black hole, which the researchers have targeted: Sagittarius A* is the largest black hole of our galaxy, the Milky Way, and is located in the center, in the direction of the constellation Sagittarius.
To capture a picture of such an incredibly distant object, astronomers created a network of eight radio telescopes. They are as far apart as possible, from Greenland to the Antarctic. So, this virtual super telescope has a diameter as big as Earth. This allows the necessary resolution and image sharpness. They would allow you to read a newspaper page in New York. The “photo” was taken in April 2017 – on one of the rare days when the weather was fine and the sky clear at all eight locations. Since then, the 200-person team has merged the data (for the hard drive in the extreme south, they had to wait until the Antarctic summer).
In 1905, Albert Einstein presented the Special Theory of Relativity, which combines space and time into four-dimensional space-time. 1915 followed the General Theory of Relativity. It explains gravity from the geometry of space-time. So far, it has withstood every test. Of course, it has to prove itself in the places of space-time where the most extreme gravitational conditions prevail: the black holes. What we think we know about them is largely derived from this theory. For the event horizon, it predicts an approximately circular shape, for the light in its vicinity a curvature.
Einstein’s theory has once again been confirmed. The assumptions and calculations used by astrophysicists have now proved themselves in an empirical experiment. So you can breathe – and keep exploring.