What are black holes?

A black hole is an extreme place in the cosmos that defies the normal notion. They can arise at the end of the development of massive stars. In a confined space an extreme mass concentrates in them. And their gravitational effect can not even escape light. Hence the name black hole.

Anything that ends up in a black hole stays there - that's the prevailing theory. So: light and matter, which once cross the so-called event horizon of the black hole, can not get outside. Even time stops inside a black hole.

What have the researchers of the Event Horizon Telescope (EHT) observed?

The team presented a picture on Wednesday at several press conferences in parallel, on which for the first time the shadow of a black hole can be seen. It comes from the galaxy Messier 87, short M87, which lies in the area of ​​the constellation Virgo. The black hole there is 55 million light-years from Earth. It has a mass of 6.6 billion solar masses. So far no one had been able to portray such a gravity monster. Instead, there were only illustrations, scientifically sometimes more and sometimes less correctly executed.

Why are the results important?

In the center of many, maybe even all galaxies, there is a black hole - but researchers have not been able to observe it yet. There is also a specimen in the heart of our Milky Way, astronomers call it Sagittarius A *. It is only about 26,500 light-years away from Earth and has a mass of about 4.1 million solar masses. It has not been shown yet, but the EHT researchers are working on it.

The basis for the theory of black holes - but they were not called that yet - was laid by Albert Einstein more than 100 years ago in his General Theory of Relativity. With the new observation, his ideas can be tested even better than before.

How did the observation succeed?

The team has interconnected eight telescopes, including the "Alma" telescope in Chile with 66 huge radio dishes, telescopes from the European Southern Observatory, also in Chile, the IRAM 30-meter telescope near Granada in the Spanish Sierra Nevada and a telescope at the South Pole.

EHT Collaboration

Original shot of black hole in galaxy M87

This is how a virtual telescope was created. Its sharpness corresponds to that of a single antenna with a diameter of 8000 kilometers. As a result, the comparatively small area of ​​a black hole can be depicted in sufficient detail. The telescopes were previously equipped, among other things with high-precision atomic clocks, so that their observations can be synchronized.

Are black holes really black?

Physicist Stephen Hawking has postulated that black holes can also release radiation from within. That is, they would lose mass over long periods of time. And they would not really be completely black. The Hawking radiation, however, has never been observed. She would only be very weak. Therefore, nobody knows at present how they can be practically demonstrated.