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The black hole is in the center of the M87 galaxy, 55 meters light from the house. Photo: Jin Liwang / Xinhua News Agency / PA Images
The revolutionary image of a black hole that adorned most of the front pages of newspapers on April 11 must be one of the most misleading scientific images of all time. This is not to impute an intentional deception to the international team of 200 astronomers who created it – it's just that nature conspires here to produce something that looks like an archetype , almost simplistic, but which in reality is a complex spectacle.
What we got is a bright yellow-orange blob with a black void in the middle: a cosmic donut in which the voracious gravitational field of the entity encompassing the light in the center had apparently dug a perfectly circular void. If you've ever imagined looking through a telescope at a black hole, you may have thought it was what you found. But you do not see what you might think, partly for deeply strange reasons.
The reason for all this enthusiasm is that this is the first time a telescope directly imitates a black hole. Black holes are stars – or in this case, vast conglomerates of many stars – that have collapsed under their own gravity. Albert Einstein's theory of general relativity, published in 1916, predicts that under certain circumstances this collapse becomes a process that continues until the objects are reduced to an infinitely small number, called singularity, where its mass becomes infinitely dense. The gravitational field created by such a dense object is so powerful that nothing can escape a certain distance (called the horizon of events) – not even light. According to Einstein's theory, what is really happening here is that the incredibly dense mass is distorting time and space itself, so that there is simply no way for light in the world. horizon of events that can come back. This is the key to the singularity of the new image: what it actually shows is not just a sphere that absorbs all the light that falls on it, but a place where time stops and space bends.
Black holes were initially considered too absurd to be believed. But from the 1960s, when research on general relativity came back into fashion in physics, it was gradually admitted that singularities could actually exist in nature and that, in fact, the universe would probably be filled black holes. In addition to those of the size of a star, formed when a large star goes out and can no longer support its own mass against inward tugging, astrophysicists have concluded that there are probably huge holes blacks of a mass of millions or billions of times larger at the center of galaxies like ours. An object in the center of our galaxy (the Milky Way) called Sagittarius A * is considered to be such a "supermassive" black hole.
Although the black holes themselves do not emit any light, virtually by definition, their presence can be inferred in different ways. The supermassive black hole at the galactic center can be inferred from the way the nearby stars seem to move, as if they were pulled by the gravity of an invisible object. In addition, the black holes suck the gas and dust inside, creating a disk-like halo of hot material that swirls a bit like a vortex of water flowing into the ground. This "accretion disk" is heated to extreme temperatures and emits radiation, mainly in the form of X and gamma rays, which can be seen by telescopes sensitive to these wavelengths. And spinning supermassive black holes at the galactic centers projects huge jets of hot gas, some of which have been seen by astronomers.
The black hole of the new image is at the center of the M87 galaxy, located 55 meters-light from the Earth. It has a mass of 6.5 billion suns, and even the dark void in the center is wider than our entire solar system. The Horizon Event Telescope (EHT), which is actually a network of eight radio telescopes around the world, interconnected and synchronized with high-precision atomic clocks to create what is actually a planet-sized telescope. Only a device of this size can zoom in on an object of this size while it is so far away. The EHT was specially set up to see this black hole of M87 and that of Sagittarius A *, much closer together but also almost a thousand times smaller. An image of this black hole in the center of our galaxy is expected shortly.
The temptation is to interpret the EHT image as a direct telescopic view of the hot accretion disk, seen from above, with the black hole digging a hole in the middle. But that's not quite right.
To begin with, it is not the visible light that is shown to us but a radiation at the edge of the radio and microwave regions of the spectrum, the white-yellow-red scale indicating its intensity. And the limit of the light and dark regions does not correspond to the event horizon, which is smaller than this: there is a gap between the inner edge of the accretion disk and the horizon of the events wherein any material is quickly sucked into the hole. . In addition, it is a composite image composed of all the data collected by the network of eight individual telescopes. The amount of information used to assemble the image itself is astronomical: it is probably the most intense scientific picture in data. The EHT network collected during its five nights of viewing in April 2017 more data than the Large Hadron Collider particle accelerator at CERN in one year, stored on half a ton of hard drives. Assembling all this data into a single image is a tour de force of computer science and uses an algorithm designed largely by graduate student Katie Bouman, while she was at the Massachusetts Institute of Technology, and Andrew Chael of Harvard. Bouman 's informal cliché on a mobile phone taken by a friend while the image was taking shape on her laptop has already become iconic – she seems to be doing something ugly transgressive.
But the most striking aspect of the picture is the donut shape. We are not just lucky enough to be on Earth in the right position to see the disc from the front. It is actually oblique. It looks like a circular ring, that's about what it would look like under most viewing angles, because the light from the back of the disc, behind the black hole, is pulled up as if it came from the top of the hole by the curved space-time that the hole creates itself.
Even if we saw the black hole thoroughly, the accretion disc would not be just a linear object, but would look like a kind of halo, although it has a sombrero shape: an image very similar to the one used for the film Interstellar, which was based on expert advice from Kip Thorne, astrophysicist Nobel laureate.
Even the fact that the ring is brighter on one side than on the other does not constitute a mere artifact of the image but a real effect, as the disc material of Accretion oscillates towards us at a speed close to that of light. one side backing away from the other. That all this corresponds to the predictions of general relativity shows once again that Einstein's theory is perfect.
You can then consider the black hole image as a sort of "real look" distortion, much like an image shot by a strange-shaped lens. But in this case, the goal is the space-time itself. Which is to say: there is no other "what would it really look like", free from such distortions – because there is no meaningful definition of reality outside of Geometric limits of space-time. Light, from this point of view, is not at all "curved": it travels all along in straight lines, but it is the sense of "right" itself that is altered by the gravity of the black hole . This That's why the image of the black hole is strangely bizarre. Once you know what you are really looking at, you realize that you do not see things hanging in space and time, but things that reshape space and time. It is a visual proof that the fabric of reality can be distorted. Bouman is right: this image is really transgressive.
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