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Understanding the Black Hole Picture Released Last Week

A reddish halo on a black background. It may not be as impressive as in science fiction movies, but this image is historical. It is the first authentic photograph of a black hole.

Provided by the collective Event Horizon Telescope, this image shows the black hole in the center of the M87 galaxy, 63 million light years away. For astronomers, it also makes it possible to see more clearly on these objects whose existence had not yet been proven.

But what does it tell us about black holes? For example, we know that the mass of this black hole is about 6.5 billion times that of our sun, a record even for a black hole. Another critical piece of information: the black hole itself measures 38 billion kilometers, or 250 astronomical units, the distance between the Sun and the Earth. The gas disc surrounding it is about 100 times larger. Vertiginous figures, in front of an image that is difficult for the ungodly to decipher.

What is a black hole?

The very nature of the black hole makes it difficult to observe them. To summarize: Black holes are astronomical objects that exist in Einstein’s theory of general relativity, and in the theory of black holes developed by successive scientists, Wheeler to Stephen Hawking. They are infinitely massive objects in the universe. Their mass is so large that absolutely nothing can escape their attraction, not even light. It makes it challenging to capture them in a photo. If their existence had not been 100% confirmed, black holes were already suspected in many parts of the universe, including the center of our galaxy.

By definition, a black hole does not return any light. To overcome this problem, astronomers seek to observe black holes by contrast. That is, by studying the contrasts and deformations on the material that surrounds it. Or, by observing the “accretion discs,” the material that accumulates around the black holes in the form of a disc and becomes extremely hot and bright. The photo of a black hole revealed by EHT is an important step forward for scientists and to confirm the functioning of this phenomenon.

What do we see on the first black hole image?

This image does not show us much at first sight. However, it allows us to be aware of several phenomena.

Reactions to this image were unanimous, in the specialized press but also in the general media and on the Internet. “The Gateway to the Universe” was the headline of the Catalan newspaper Ara, for example. The progress also moved scientists that this image represents. “We have succeeded in transforming a mathematical tool into a physical object that can be tested, observed and measured,” explained one of the speakers at the press conference where the image was unveiled.

A second image was also unveiled. This one shows a much broader plane of the black hole. While the “hole” itself is much less evident in this photo, it is a much more impressive picture of the gas and overheated matter in the center of the M87 galaxy. Taken by the Chandra telescope, it is also much more vertiginous: our solar system could fit in the black spot in the center of the box in the photo. Scientists hope that this image, combined with the new Event Horizon Telescope photo, will provide much more information about black holes.

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