The black hole image validates the imagination of the unimaginable

Black holes capture everything that they encounter. From subatomic particles to stars, through solids, gases, liquids and even light, everything falls irremediably. And even more assuredly, black holes capture the popular imagination.

Thinking about space, as humans have done since they first observed the points of light decorating the night sky, brings the mind to imagine things that can not be lived here on earth. And black holes widen the imagination more dramatically than any other wonder that astronomy has to offer. A black hole is a cosmic vacuum, sucking star dust into the purest of bottomless pits, a space-time contortion exerting an irresistible gravitational attraction, a nothingness capable of erasing everything. It's a hole in space, dark because light can not escape its appeal. It is therefore invisible. Hard to imagine.

Yet, black holes have been imaginable for a long time, even though no one knew they were real. In 1784, the English geologist and ecclesiastic (and amateur astronomer) John Michell assumed that for a star large enough and dense enough, the Newtonian gravity would be too strong for the light to escape. He believed (like Newton) that light is a flow of particles (as was commonly accepted at this time). Michell calculated that the speed of light particles would be insufficient to escape the gravity of a star as dense as the sun but 500 times its diameter. "Their light could not happen to us," he writes.

A decade later, the French mathematician Pierre-Simon Laplace also hypothesized that "invisible bodies" could exist in space. Laplace is considered a star with the density of the Earth and 250 times wider than the sun. Its Newtonian gravitational attraction would not allow the light to leave its surface. "The largest bodies in the universe can therefore be invisible because of their size," he said. (You can read a detailed account of Michell's and Laplace's black hole papers in the Journal of Astronomical History and Heritage.)

True black holes do not come out of Newtonian gravity, but from Einstein's theory of gravity – general relativity. Einstein has hidden black holes (even of himself) in his equations. But the German astronomer Karl Schwarzschild dismissed the concept of these equations during the First World War, shortly before his death after falling ill on the Russian front. Schwarzschild, however, was unable to imagine that a star could shrink enough to exceed the density needed to make it invisible. This no imagination came from J. Robert Oppenheimer and Hartland Snyder in 1939 (the same year, Einstein wrote an article denying the existence of black holes). Oppenheimer and Snyder calculated that a sufficiently massive star would collapse under its own gravity. "The star tends to isolate itself from all communication with a distant observer; only his gravitational field persists, "they wrote.

Oppenheimer quickly took over the Manhattan project for the construction of the atomic bomb and no one paid much attention to his collapsed stars until the 1960s. They were discussed at a symposium in Dallas in December. 1963 and a few weeks later at a meeting in Cleveland. Someone even pronounced the phrase "black hole" to refer to it. (The first astrophysical use of this term in print appeared in Science News LetterCover of the Cleveland meeting in the January 18, 1964.)

But the name "black hole" was not understood until John Archibald Wheeler used it during a speech in 1967. The scientific study of black holes then began in earnest. Stephen Hawking studied them, showing that they could actually emit a weak form of radiation since his name. Astronomers have searched for them, collecting impressive evidence of their existence, based on the movement of stars and other nearby materials. (Michell, in fact, had suggested this approach to detect the presence of an invisible star.) In 2016, gravitational waves provided a clear sign of the collision of two black holes.

So, almost no one now doubts their existence. But while Michell, Oppenheimer, Wheeler, Hawking and many others imagined what a black hole should look like, none of them had ever seen one.

Now, however, the Event Horizon Telescope collaboration has provided an image of the darkness of the black hole surrounded by the unimported light nearby. This image confirms what we already knew, namely that black holes are not mere products of the imagination, but truths initially imagined by minds imbued with a certain scientific spirit – the belief in the ability to discover things in the space without going there.

The history of science records other cases of imagination of phenomena that defy the imagination before proving their discovery. Paul Dirac imagined antimatter before anyone found it in nature. Alexander Friedmann imagined the expansion of the universe before the astronomical observations confirm it. The philosophers of ancient Greece imagined atoms 2,500 years before microscopy became sophisticated enough to take their picture. All these successful imaginations had been regarded by some as an affront to common sense or conventional logic. Their confirmations, as with the new black hole image, reinforce the lesson that apparent absurdity is not a valid argument against existence.

Perhaps the fact that the human imagination has designed black holes, despite the veracity of their absurdity, is one of the reasons they captivate the imagination of almost all people whose brain, as Carl Sagan would say, is not wooden.

Black holes have consumed the mental energy of the great physicists, astronomers and mathematicians of the world, revealed secrets about objects in space and space-time itself, fascinated the general public, inspired books and films science-fiction and illustrated the fantastic magnitude of nature's (and destructive) creatives. The black hole has become the child of posters for astronomical phenomena outrageously incomprehensible.

And now, there is an image available to put on the poster.

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