The cloud of mystery surrounding the heart of our galaxy has finally dissipated; On the morning of May 12, 2022, the astronomers behind the project… event horizon telescopeEHT) Several press conferences at the same time in different regions of the world, in which they moved The unveiling of the first image of the supermassive black hole “Sagitarias A .” The star Sagittarius A*which is located in the center of our galaxy, this is not The first image taken by this collaborative project of a black hole was preceded by the famous image of M87*, which was revealed on April 10, 2019. But this new image is what the project’s astronomers desperately wanted. the hole “Sagitarias a StarIt is the supermassive black hole in our galaxy, and the fixed point that revolves around the galaxy.
Scientists have long believed that a supermassive black hole lurking deep in the turbulent heart of our galaxy is the only possible explanation for the oddities that lie in that region, such as giant stars accelerating around a hidden object in space there, at a speed estimated at a significant percentage of the speed of light, but scientists were reluctant to say With this hypothesis; For example, when astronomers Reinhard Genzel and Andrea Geis shared the 2020 Nobel Prize in Physics, for their research on wormholes,Sagittarius A Star”Her statement of honor stated that they won the prize for “discovering a dense, supermassive object at the center of our galaxy”, not for discovering a “black hole”, but there is no room for such reservations now.
On the morning of May 12th at the National Press Club in Washington, D.C., Ferial Ozil – Professor of Astronomy and Physics at the University of Arizona, and a member of the Scientific Council of the Project “…event horizon telescopeAbout the image of our galaxy’s black hole, which appears to be a dark ring, surrounded by three bright nodes of gas with a temperature of a trillion degrees Celsius, and Ozil said, commenting on this image: “I knew with ‘Sagittarius A Star‘ Twenty years ago, and I loved him and tried to understand him since, but we don’t have a direct picture of him yet.”
Black holes trap everything that falls within them, including light, so they are virtually invisible, but they change the nature of space-time around them so severely that they become a “shadow” when illuminated by the glowing flows of material falling within them as they rip under the weight of their gravity, this shadow is About two and a half times larger than the black hole’s “event horizon”, which is the hole’s outer boundary and hallmark, the line of spacetime from which nothing can ever return.
The Event Horizon Telescope project depicts this shadow using very long baseline interferometry, or VLBI, a technique that combines radio observatories located on different continents, to form a hypothetical Earth-size telescope, with the highest accuracy among astronomical observation tools. All of them, and in April 2017, he spent the “Project”event horizon telescope The co-op several nights as it points this virtual telescope towards “Sagitarias a StarAnd towards other supermassive black holes, and we have already seen before the first end results of that effort, which is the image of the hole “M87 Star”.، During those efforts, the team also collected raw data about “Sagitarias A Star”, It took much longer, however, to convert those observations into an actual image.
This is due to the constant change that takes place “Sagitarias A Star”; The hole “M87 Star” – located in the heart of a galaxy.Messier 87″ Messier 87, or M87 for short, is so huge that matter orbiting around it takes many hours to complete a complete revolution, which means, in practical terms, that you can stare at it for a long time without changing anything. “Sagitarias A Star” It has more than 1,000 times less mass, so it’s changing about 1,000 times faster than it does, as matter moves around the hole faster and its orbits shrink, says Katie Bowman, a computer scientist and astronomer at Caltech, who co-led the imaging team. within the projectevent horizon telescope: Matter revolves around “Sagitarias A Star” So fast that it changes “from minute to minute.” Imagine using time-lapse technology to take a photograph of a fast-moving bullet. This is not easy, so extracting a clear picture of the hole”Sagittarius A Star” From the data collected during the 2017 monitoring round required several years of work.
But just as the changing nature of this black hole makes it difficult to spot, it also makes it an exciting laboratory for future studies of black holes and Einstein’s general theory of relativity, his much-interested theory of gravity, although astronomers already knew the basic measurements. To our galaxy’s black hole With high accuracy (its mass, diameter, and distance from the ground)، Thanks to decades of studying it with all kinds of telescopes, they can now finally see it as it mutates, feeding on streams of bright, glowing matter.
breaking through the veils
Scientists began suspecting a black hole lurking at the heart of our galaxy in the early 1960s, shortly after the discovery of active galactic nuclei, which are ultra-bright regions at the centers of some galaxies that are illuminated by omnivorous supermassive black holes. The surface of the earth, active galactic nuclei are considered ancient, we only see them in regions of the universe very far from us, so where did all these nuclei go? In 1969, the English astrophysicist Donald Linden-Bell argued that these nuclei were not going anywhere, but were now sleeping after their fatty meals. He predicted that there are inert supermassive black holes all around us in the centers of spiral galaxies, and from Including our galaxy.
In 1974, American astronomers Bruce Balick and Robert Brown used radio telescopes located in the Green Bank region of West Virginia, and directed them towards the center of the Milky Way, to discover a dark spot that they suspected to be the central black hole of our galaxy, the two scientists found this spot in an area of the sky it’s called “Sagitarias eh?Sagittarius A, and the radiation emitted from this new source was illuminating the nitrogen clouds surrounding it, or excite them, so Brown used the naming method used in atomic physics, in which excited atoms are distinguished by adding an “asterisk” to it, and he called the newly discovered spot the name “Sagitarias eh? Star” Sagittarius A*.
Then, over the next two decades, radio astronomers gradually improved their observations of this object, but their attempts were limited by the unavailability of suitable telescopes, the relatively primitive techniques they used (they were as primitive as cassette tapes to us now), and the difficulty of observing the galactic center by its nature .
Disappears “Sagitarias eh? “A curtain” behind a multi-layered veil, the first of which is known as the galactic plane, which is gases and dust extending for a distance of 26,000 light years, and obscuring visible light. The scattering barrier, a turbulent patch of space where radio waves are deflected by density changes in interstellar space. “Sagitarias A Star” It is the mortal matter surrounding the black hole itself, and trying to stare at the black hole through those barriers is a bit like peeling an onion, and since the outer layers surrounding the black hole emit light of longer wavelengths, this means that if the VLBI technique could be used to observe If the light rays have smaller wavelengths, it will be possible to take pictures closer to the event horizon of a black hole, but achieving this has been a major technological challenge.
At first, astronomers using other techniques, interferometry, had more success, as they kept collecting indirect evidence that the Sagittarius-A star spot was in fact an erupting supermassive black hole; In the 1980s, physicist Charles Townes and his colleagues showed that the clouds of gas in the center of the galaxy were moving in a way that could only be explained by the influence of a huge, invisible gravitational mass. Then, in the 1990s, Geese and Genzel separately began tracking the orbits of giant blue stars in the center of the galaxy. and monitor its movement around a heavy but invisible focal point.
Meanwhile, the situation has improved for radio astronomers; The late 1990s and early 2000s saw the start of a new generation of high-frequency radio telescopes, which if backed by a lot of specially designed equipment could participate in observations with the technique of interferometry at microwave frequencies that are believed to be radiating from the edge of the shadow “Sagitarias eh? Star.” At the same time, thanks to the computing revolution that led to the emergence of hard drives and the proliferation of smartphones, the amount of data that each observatory in networks of radio telescopes could record and process had increased exponentially.
In 2007, a former small project of the “Project”event horizon telescope Among these developments; He used three telescopes in Hawaii, California and New Mexico to penetrate the veil surrounding Sagittarius-A-star, and although the project made little progress in capturing an image of the black hole, it detected “something”.
Scientists have known for some time that black holes are supposed to have visible shadows under certain conditions. In 1973, physicist James Bardeen predicted that silhouettes of black holes would appear if they were found against a bright background, but Bardeen saw “there does not seem to be any hope of observing this effect.” Then, in 2000, astrophysicists Hino Valcke explained Fulvio Melia and Eric Agul suggest that if an Earth-sized radio telescope collecting microwaves were available, it should be able to detect a shadow “Sagitarias eh? Star”, caused by the glow of the surrounding ring of fragmentation.
About five years later, a few dozen astronomers and astrophysicists hard at work in this mysterious field of astronomy agreed on a specific goal: to create a hypothetical radio telescope the size of Earth to observe that shadow, and the meeting took place. The inaugural project for this project took place in January 2012, and the . project was born event horizon telescope.
Five years later, after the project had evolved into a collaborative project involving more than 200 scientists, involving eight observatories from around the world, the team made the first real attempt to monitor the shadow of “Sagitarias eh? Star.” Over the course of ten days in April 2017, telescopes in North America, South America, Hawaii, Europe and Antarctica all focused their lenses on the galactic center and other black holes, collecting 65 hours of data on 1,024 hard disks. Each was eight terabytes, and the disks were then shipped to supercomputer data repositories in Massachusetts and Germany to search for any correlations. The project The whole world was delighted for the success of their experience, and commenting on this achievement, Bowman said on the morning of the 12th of May when the photo was revealed: “We have been working on this project for a very long time, to the point that one has to pinch himself from time to time to make sure that it is not a dream, this It is the black hole at the center of our galaxy!