Black holes take over everything they collide with. From subatomic particles to stars, solids, gases, liquids, and even light, whatever falls in them disappears. Similarly, black holes capture the popular imagination. Thinking about space, ever since humans first saw the points of light that adorn the night sky, has made the mind imagine things that cannot be seen here on Earth. And black holes are more imaginative than any other marvel of astronomy.
What does a black hole look like?
A black hole is a space vacuum cleaner that sucks stardust into the most bottomless abyss, bends space-time, causing an irresistible gravitational attraction, nothingness that can wipe everything off the face of the earth.
This is a hole in space. Black - because light cannot escape its attraction. And therefore invisible. Unimaginable.
And yet they tried to imagine black holes - even before they knew that they really exist. In 1784, English geologist and clergyman (and amateur astronomer) John Michell suggested that for a large and dense enough star, Newtonian gravity would be too strong for light to escape. He believed (like Newton) that light is a stream of particles (then many thought so). Michell calculated that the speed of light particles would not be sufficient to avoid the gravity of a star as dense as the sun but 500 times its diameter. "Such light cannot come to us," he wrote.
About ten years later, the French mathematician Pierre-Simon Laplace also suggested that "invisible bodies" could exist in space. Laplace imagined a star with the density of the Earth and 250 times wider than the sun. Its Newtonian gravitational pull would prevent light from leaving the surface. “Thus, the largest bodies in the universe can be invisible due to their size,” he said.
Real black holes do not arise from Newtonian gravity, but from Einstein's theory of gravity - general relativity. Einstein hid black holes (even from himself) in his equations. But German astronomer Karl Schwarzschild used this concept during World War I, shortly before dying after an illness on the Russian front. Schwarzschild, however, could not imagine that a star could shrink to such an extent that it exceeded the density required to render it invisible. This feat of imagination was accomplished by Robert Oppenheimer and Heartland Snyder in 1939 (the same year that Einstein published a paper in which he denied the existence of black holes). Oppenheimer and Snyder calculated that a sufficiently massive star could collapse under its own gravity.“Thus, the star will be closed from any connection with a distant observer; only the gravitational field will remain,”they wrote.
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Oppenheimer soon took up the Manhattan Atomic Bomb Project, and no one paid much attention to its collapsing stars until the 1960s. In December 1963, they were discussed at a symposium in Dallas, and a few weeks later at a meeting in Cleveland. Someone even uttered the phrase "black hole" to refer to them.
But the name was not popular until John Archibald Wheeler pronounced it in a speech in 1967. Then serious scientific research on black holes began. Stephen Hawking studied them, showing that they could emit a weak form of radiation that was named after him. Astronomers are looking for black holes, collecting impressive evidence that they do exist, based on the movement of stars and other substances in the vicinity of black holes. (In fact, Michell proposed just such an approach for detecting the presence of an invisible star.) In 2016, gravitational waves provided accurate evidence of a collision of two black holes.
Now, almost no one doubts that they exist. But although Michell, Oppenheimer, Wheeler, Hawking, and many others imagined what a black hole should be like, none of them had ever seen it.
And now, literally in April, the Event Horizon Telescope collaboration presented an image: the darkness of a black hole surrounded by light in its vicinity. This image confirms what was already known: that black holes are not just a figment of the imagination, it is a truth originally represented by minds imbued with a certain scientific spirit, a belief in the ability to discover cosmic phenomena without ever being in space.
The history of science remembers other cases of imaginary phenomena that defy imagination even before their discovery. Paul Dirac imagined antimatter even before it was found in nature. Alexander Friedman imagined the expansion of the universe before astronomical observations confirmed it. Ancient Greek philosophers imagined atoms 2,500 years before microscopy became sophisticated enough to photograph them. All these lucky fantasies were regarded by some as an insult to common sense or conventional logic. Their confirmation, as with the new image of the black hole, confirms the lesson that apparent absurdity is not a convincing argument against the existence of a phenomenon.
Perhaps the fact that the human imagination has led to the existence of black holes, despite their absurdity, is one of the reasons why black holes fascinate anyone who thinks of them. The black hole has become proof of the existence of incredibly incomprehensible astronomical phenomena.
Ilya Khel
