Looking at the two images, one wonders if the researchers aren't disappointed.

Isn't one almost the same as the other?

But the orange-hued radio emission shadow of the black hole at the center of galaxy M87 graced front pages in 2019, as did that of Sagittarius A* at the navel of the Milky Way this Friday.

One is generated by six billion solar masses in a volume the diameter of our solar system, the other hides the mass of four million suns in an area that would fit within the orbit of Mercury, the planet closest to the sun.

In one case, plasma streams in from the outside like a cataract, in the other with the force of a dripping water tap.

Ulf von Rauchhaupt

Editor in the “Science” section of the Frankfurter Allgemeine Sunday newspaper.

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But precisely because of this, the meaning of the new image lies precisely in its resemblance to the old one.

"Now we know that it was no coincidence," said astrophysicist Feryal Özel from the University of Arizona on Thursday in Washington at the press conference of the American part of the research collaboration "Event Horizon Telescope" (EHT).

"There was nothing in the area that happened to make the picture look like the ring we were expecting," Özel continued.

"The two images are similar because they are the result of fundamental effects of gravity." Einstein's theory of gravity was again stupendously confirmed in one of the most extreme regimes accessible to observation today - but over three orders of magnitude.

Because there are definitely alternative ideas that try to explain the concentration of such enormous masses in such small volumes, without a black hole with its event horizon - i.e. a limit beyond which nothing can get out that once got inside.

But many of these ideas are now also obsolete for Sagittarius A*: "We can rule out bare singularities and wormholes," says Luciano Rezzolla from the University of Frankfurt.

Naked singularities, that would be points of infinite space curvature without a veiling event horizon, and wormholes would be tunnel-like shortcuts through space-time.

Dealing with the effects of such hypothetical structures is one of the specialties of Rezzolla and his group, who study the behavior of radiation,

Hardly any chances for Gravastars

Neither M87* nor Sagittarius A* can be behind so-called grava stars - spheres from "false vacuum" that were specially devised so that one does not have to believe in black holes.

"At least in their usual formulations," says Luciano Rezzolla.

The central shadow would be less pronounced there, as the inflowing matter would reach a surface and radiate there.

"But the people who like grava stars have also come up with something here: It could be that the matter does not accumulate on the surface but is absorbed, like water that falls on sand and seeps away."