We are facing a new historical image for our knowledge of the Universe. Three years after that of M87, we can see another “photo” of a black hole: the one in the center of the Milky Way. This time it is a recovery in some ways more exciting, because it is “our” supermassive giantin short, the one that sits in the heart of our galaxy.
Sagittarius A * finally has a face, or rather, a shadow, drawn by the incandescent gases that orbit its cesspool. It was unveiled today during a simultaneous worldwide press conference at the headquarters of the European southern observatory, in Germany, from the international collaboration of the Event horizon telescope (Eht): the same that, in 2019, had disclosed the first image of one of these mysterious celestial objects, the black hole at the center of the galaxy M87. And thanks to this observation Albert Einstein’s theory of relativityonce again tested, it held up.
A great international effort was required to achieve this result, theEht gathers dozens of research institutes (including MIT, the Max Planck Institute and the Smithsonian Astrophysical Observatory in Cambridge) and about 300 scientists from all over the world. They used it the Very Long Baseline Interferometry technique (Very Wide Base Interferometry): An array of eight radio telescopes on different continents which, together, have composed a virtual parabola the size of the whole planetnecessary to be able to “solve” an object so distant and small, at least seen from here.
It is as if the scientists have focused a tennis ball on the surface of the Moon as seen from Earth. For Italy, the National Institute of Astrophysics (Inaf), the National Institute of Nuclear Physics (Infn), the University of Cagliari and the Federico II University of Naples contributed.
On the edge of space and time
It took much longer to compose and focus the pieces of light coming from the surroundings of Sagittarius A *, because it has a more fickle demeanor and hides behind a thick layer of dust. It is not about light that we could see with our eyes but about radio waves, which can reach us “Piercing” the curtain surrounding the galactic center. However, it is a snapshot of what happens at the edge of the knowable, beyond which time and space cease to exist as we understand them.
Space
Why it took five years to ‘develop’ the first photo of the black hole Sagittarius A *
by Matteo Marini
12 Maggio 2022
Eventually, her silhouette emerged brilliant thanks to thering of gas surrounding itaccelerated and heated by the very high gravitational pull of the giant, whose mass is four million times that of the Sun.. Inside that cesspool is the event horizon from which nothing, not even light, can come out after crossing the border.
“Three years ago everyone expected to see Sagittarius A * earlier than M87, but there were problems that required more time to analyze data, calibrate observations and obtain images – says Elisabetta Liuzzo, Inaf researcher at the Institute of radio astronomy in Bologna and Eht member – problems due to the fact that it is very variable, there is more interstellar medium, dust and gas that distort the signal ”. Liuzzo presented the results of the observation in an event at the headquarters of the National Institute of Astrophysics (INAF) in Rome.
Einstein’s Relativity explains everything
Again, we have ahead a ring of light embracing a circle of darknessthe shape and dimensions predicted thanks to Einstein’s theory of general relativity.
A theory that once again stands the test of observation, because Sagittarius A * has long been studied indirectly: “We can say more: Sagittarius A * has a huge advantage over M87. By observing the trajectories of the stars that orbit around it, its mass had already been calculated very well – explains Ciriaco Goddi, astrophysicist at the University of Cagliari, associated with INAF and member of the Eht collaboration – and if we measure the size of the shadow from the image , which is two and a half times the event horizon, we can also calculate the mass using general relativity ”. And the accounts add up with the previous estimate: Relativity also works here, in the most extreme conditions. This precision was not achieved with the black hole M87.
Elisabetta Liuzzo worked on cleaning up the raw data, in particular the distortions induced by the atmosphere that the waves must pass through to be collected by the large parabolas of radio telescopes. He can finally present the fruit of five years of work: “From the astronomical point of view we are observing a result that will have a great impact, it is a great satisfaction. Even more so because we are looking at something that belongs to our galaxy, a black hole at its center influences the evolution of the entire Milky Way, the system in which we ourselves live ”.
What is Sagittarius A *
The one in the center of the Milky Way is the closest supermassive black hole to us, it is about 26,000 light years away.
The diameter of Sagittarius A * (the asterisk indicates the source of radio waves) according to estimates, is greater than 44 million light years and has a mass equal to four million times that of the Sun. However, it is not even comparable to the supermassive black hole “photographed” three years ago always using Eht.
In fact, at the center of the galaxy M87 resides a monster whose size exceeds six billion Suns. It is nearly two thousand times larger than Sagittarius A *. Also for this reason, seen from the terrestrial instruments, despite being much further away, they appear of similar dimensions.