The date of May 12, 2022 is to be branded in the history of the study of the cosmos. Astronomers have revealed the very first image of Sagittarius A*, the supermassive black hole at the center of our galaxy, the Milky Way.
A scientific feat
This historic image is the result of five years of astronomical work. More than 300 researchers from around the world worked together to collect the data needed to create the image. They had access to its data through a planetary network of radio telescopes located around the world and called Event Horizon Telescope (EHT).
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The image was revealed during six simultaneous press conferences, and gives us a glimpse of the monster at the center of our galaxy, 27,000 light years from Earth. As the scientists explained in their lecture, this is equivalent to observing a crescent-sized object on the surface of the Moon from Earth.
Of course the image does not show the black hole itself; no light can escape, making it invisible. Rather, the EHT is able to see light as radio waves and was thus able to capture these waves from hot gases swirling around the edge of the event horizon, the place of no return from which more nothing can escape from the black hole. The latter feeds on the matter present in its immediate environment, be it gas clouds, asteroids or even stars that could approach too close and be torn apart by its gravitational forces.
Gas, dust, or even jagged stars that fall into a black hole are thus heated to millions of degrees in a swirling current of electromagnetic fields; some of this material falls into the black hole, but some is ejected by enormous pressures and magnetic fields.
This is not the first image of a black hole
As extraordinary as it is, this image is not the first image of a black hole. In 2019, the EHT was indeed able to capture a visual of M87*, a supermassive black hole housed in the center of the M87 galaxy. However, the image of Sagittarius A*, although it is much closer to us than M87*, was more complicated to obtain.
This is because the gas surrounding Sagittarius A* completes an orbit in just minutes, compared to days or weeks for the gas orbiting the much larger M87*, resulting in a rapid change in brightness. and the gas configuration, specifies the MIT Technology Review. The team of researchers compared the capture of this phenomenon to ” the attempt to take a clear photo of a puppy rapidly chasing its tail “.
Because, if the two black holes observed are supermassive, they are absolutely not the same size. Sagittarius A* is roughly the length of Mercury’s orbit around the Sun, and its mass is 4 million times that of our star. M87* is equivalent to 6.5 billion solar masses. To compare the two black holes, a researcher from the group said during the press conference that if Sagittarius A* were a doughnut, M87* would be the size of a football stadium like the Allianz Arena in Munich.
The image of the supermassive black hole M87*, captured in 2019, showing a monster with a mass equivalent to 4.5 billion times that of the Sun. Image: EHT Collaboration
Einstein’s general relativity is confirmed once again
From a scientific point of view, the researchers’ announcement is fabulous. The existence of black holes was predicted by calculations by Albert Einstein in his theory of general relativity. The latter described a new conception of the cosmos in which spacetime can quiver, bend, tear, expand, swirl and even disappear forever into a black hole, an object whose gravity is so strong that nothing, nor even light can escape it.
This theory seemed so crazy to Einstein that he did not believe it and was convinced that he had made a mistake. Now, two of them have been immortalized in the center of galaxies; this gives reason to the calculations of the scientist, and also confirms the thesis of the scientists, who estimate that almost all the galaxies shelter in their center a supermassive black hole. Moreover, if the existence of Sagittarius A* was assumed, with numerous supporting evidence, by researchers; it is now confirmed.
The astronomers were also struck by the resemblance between the two black holes, which are however in the middle of two galaxies completely different, in size and shape. As a reminder, there are many black holes within the Milky Way, but they are often the remnants of dead stars that have collapsed in on themselves. Supermassive black holes, on the other hand, are incredibly larger objects, so much so that scientists don’t know how they got there.
We still have many mysteries to solve about these fascinating stars, including how they form, and why they are at the center of galaxies, causing the stars that make up the latter to orbit around them (yes, the Sun orbits around Sagittarius A* as the Earth orbits around the Sun). Thanks to the Event Horizon Telescope, it is certain that the years to come will be rich in discoveries about the most enigmatic objects in the Universe.